Update the mlx.launch and mlx.distributed_config docs

.github/actions/build-cuda-release/action.yml

@@ -1,6 +1,15 @@
 name: 'Build CUDA wheel'
 description: 'Build CUDA wheel'
 
+inputs:
+  arch:
+    description: 'Platform architecture tag'
+    required: true
+    type: choice
+    options:
+      - x86_64
+      - aarch64
+
 runs:
   using: "composite"
   steps:
@@ -12,4 +21,4 @@ runs:
         pip install auditwheel build patchelf setuptools
         python setup.py clean --all
         MLX_BUILD_STAGE=2 python -m build -w
-        bash python/scripts/repair_cuda.sh
+        bash python/scripts/repair_cuda.sh ${{ inputs.arch }}

.github/actions/setup-linux/action.yml

@@ -15,6 +15,7 @@ runs:
   using: "composite"
   steps:
     - name: Use ccache
+      if: ${{ runner.arch == 'x86_64' }}
       uses: hendrikmuhs/ccache-action@v1.2
       with:
         key: ccache-${{ runner.os }}-${{ runner.arch }}-${{ inputs.toolkit }}-py${{ inputs.python-version }}

.github/workflows/release.yml

@@ -128,7 +128,11 @@ jobs:
 
   build_cuda_release:
     if: github.repository == 'ml-explore/mlx'
-    runs-on: ubuntu-22-large
+    strategy:
+      matrix:
+        arch: ['x86_64', 'aarch64']
+        toolkit: ['cuda-12.9', 'cuda-13.0']
+    runs-on: ${{ matrix.arch == 'x86_64' && 'ubuntu-22-large' || 'ubuntu-22-large-arm' }}
     env:
       PYPI_RELEASE: 1
       DEV_RELEASE: ${{ github.event.inputs.dev_release == 'true' && 1 || 0 }}
@@ -136,9 +140,11 @@ jobs:
       - uses: actions/checkout@v6
       - uses: ./.github/actions/setup-linux
         with:
-          toolkit: 'cuda-12.9'
+          toolkit: ${{ matrix.toolkit }}
       - name: Build Python package
         uses: ./.github/actions/build-cuda-release
+        with:
+          arch: ${{ matrix.arch }}
       - name: Upload artifacts
         uses: actions/upload-artifact@v5
         with:

docs/src/install.rst

@@ -29,17 +29,20 @@ MLX has a CUDA backend which you can install with:
 
 .. code-block:: shell
 
-    pip install mlx[cuda]
+    pip install mlx[cuda12]
+
 
 To install the CUDA package from PyPi your system must meet the following
 requirements:
 
-- Nvidia architecture >= SM 7.0 (Volta)
+- Nvidia architecture >= SM 7.5
 - Nvidia driver >= 550.54.14
 - CUDA toolkit >= 12.0
 - Linux distribution with glibc >= 2.35
 - Python >= 3.10
 
+For CUDA 13 use ``pip install mlx[cuda13]``. The CUDA 13 package requires
+an Nvidia driver >= 580 or an appropriate CUDA compatibility package.
 
 CPU-only (Linux)
 ^^^^^^^^^^^^^^^^

docs/src/usage/distributed.rst

@@ -7,22 +7,29 @@ Distributed Communication
 
 MLX supports distributed communication operations that allow the computational cost
 of training or inference to be shared across many physical machines. At the
-moment we support three different communication backends:
+moment we support several different communication backends introduced below.
+
+.. list-table::
+   :widths: 20 80
+   :header-rows: 1
+
+   * - Backend
+     - Description
+   * - :ref:`MPI <mpi_section>`
+     - A full featured and mature distributed communications library.
+   * - :ref:`RING <ring_section>`
+     - Ring all reduce and all gather over TCP sockets. Always available and
+       usually faster than MPI.
+   * - :ref:`JACCL <ring_section>`
+     - Low latency communication with RDMA over thunderbolt. Necessary for
+       things like tensor parallelism.
+   * - :ref:`NCCL <nccl_section>`
+     - The backend of choice for CUDA environments.
 
-* `MPI <https://en.wikipedia.org/wiki/Message_Passing_Interface>`_ a
-  full-featured and mature distributed communications library
-* A **ring** backend of our own that uses native TCP sockets. It should be
-  faster for thunderbolt connections, but it also works over Ethernet.
-* `nccl <https://developer.nvidia.com/nccl>`_, for use in CUDA environments.
 
 The list of all currently supported operations and their documentation can be
 seen in the :ref:`API docs<distributed>`.
 
-.. note::
-   Some operations may not be supported or not as fast as they should be.
-   We are adding more and tuning the ones we have as we are figuring out the
-   best way to do distributed computing on Macs using MLX.
-
 Getting Started
 ---------------
 
@@ -85,7 +92,7 @@ Selecting Backend
 ^^^^^^^^^^^^^^^^^
 
 You can select the backend you want to use when calling :func:`init` by passing
-one of ``{'any', 'ring', 'mpi', 'nccl'}``. When passing ``any``, MLX will try all
+one of ``{'any', 'ring', 'jaccl', 'mpi', 'nccl'}``. When passing ``any``, MLX will try all
 available backends. If they all fail then a singleton group is created.
 
 .. note::
@@ -110,6 +117,8 @@ The following examples aim to clarify the backend initialization logic in MLX:
     world_ring = mx.distributed.init(backend="ring")
     world_any = mx.distributed.init()  # same as MPI because it was initialized first!
 
+.. _training_example:
+
 Training Example
 ----------------
 
@@ -192,16 +201,273 @@ almost identical to the example above:
         loss = step(model, x, y)
         mx.eval(loss, model.parameters())
 
+.. _ring_section:
+
+Getting Started with Ring
+-------------------------
+
+The ring backend does not depend on any third party library so it is always
+available. It uses TCP sockets so the nodes need to be reachable via a network.
+As the name suggests the nodes are connected in a ring which means that rank 1
+can only communicate with rank 0 and rank 2, rank 2 only with rank 1 and rank 3
+and so on and so forth. As a result :func:`send` and :func:`recv` with
+arbitrary sender and receiver is not supported in the ring backend.
+
+Defining a Ring
+^^^^^^^^^^^^^^^
+
+The easiest way to define and use a ring is via a JSON hostfile and the
+``mlx.launch`` :doc:`helper script <launching_distributed>`. For each node one
+defines a hostname to ssh into to run commands on this node and one or more IPs
+that this node will listen to for connections.
+
+For example the hostfile below defines a 4 node ring. ``hostname1`` will be
+rank 0, ``hostname2`` rank 1 etc.
+
+.. code:: json
+
+    [
+        {"ssh": "hostname1", "ips": ["123.123.123.1"]},
+        {"ssh": "hostname2", "ips": ["123.123.123.2"]},
+        {"ssh": "hostname3", "ips": ["123.123.123.3"]},
+        {"ssh": "hostname4", "ips": ["123.123.123.4"]}
+    ]
+
+Running ``mlx.launch --hostfile ring-4.json my_script.py`` will ssh into each
+node, run the script which will listen for connections in each of the provided
+IPs. Specifically, ``hostname1`` will connect to ``123.123.123.2`` and accept a
+connection from ``123.123.123.4`` and so on and so forth.
+
+Thunderbolt Ring
+^^^^^^^^^^^^^^^^
+
+Although the ring backend can have benefits over MPI even for Ethernet, its
+main purpose is to use Thunderbolt rings for higher bandwidth communication.
+Setting up such thunderbolt rings can be done manually, but is a relatively
+tedious process. To simplify this, we provide the utility ``mlx.distributed_config``.
+
+To use ``mlx.distributed_config`` your computers need to be accessible by ssh via
+Ethernet or Wi-Fi. Subsequently, connect them via thunderbolt cables and then call the
+utility as follows:
+
+.. code:: shell
+
+   mlx.distributed_config --verbose --hosts host1,host2,host3,host4 --backend ring
+
+By default the script will attempt to discover the thunderbolt ring and provide
+you with the commands to configure each node as well as the ``hostfile.json``
+to use with ``mlx.launch``. If password-less ``sudo`` is available on the nodes
+then ``--auto-setup`` can be used to configure them automatically.
+
+If you want to go through the process manually, the steps are as follows:
+
+* Disable the thunderbolt bridge interface
+* For the cable connecting rank ``i`` to rank ``i + 1`` find the interfaces
+  corresponding to that cable in nodes ``i`` and ``i + 1``.
+* Set up a unique subnetwork connecting the two nodes for the corresponding
+  interfaces. For instance if the cable corresponds to ``en2`` on node ``i``
+  and ``en2`` also on node ``i + 1`` then we may assign IPs ``192.168.0.1`` and
+  ``192.168.0.2`` respectively to the two nodes. For more details you can see
+  the commands prepared by the utility script.
+
+.. _jaccl_section:
+
+Getting Started with RDMA over Thunderbolt
+------------------------------------------
+
+Starting from version 26.2 RDMA over thunderbolt is available in MacOS and
+enables low-latency communication between Macs with thunderbolt 5. MLX provides
+the JACCL backend that uses this functionality to achieve communication latency
+an order of magnitude lower than the ring backend.
+
+.. note::
+
+   The name JACCL (pronounced Jackal) stands for *Jack and Angelos' Collective
+   Communication Library* and it is an obvious pun to Nvidia's NCCL but also
+   tribute to *Jack Beasley* who led the development of RDMA over Thunderbolt
+   at Apple.
+
+Enabling RDMA
+^^^^^^^^^^^^^
+
+Until the feature matures, enabling RDMA over thunderbolt is slightly more
+involved and **cannot** be done remotely even with sudo. In fact, it has to be
+done in macOS recovery:
+
+1. `Start your computer in recovery <https://support.apple.com/en-us/102518>`_.
+2. Open the Terminal by going to Utilities -> Terminal.
+3. Run ``rdma_ctl enable``.
+4. Reboot.
+
+To verify that you have successfully enabled Thunderbolt RDMA you can run
+``ibv_devices`` which should produce something like the following for an M3 Ultra.
+
+.. code-block:: bash
+
+    ~ % ibv_devices
+    device          	   node GUID
+    ------          	----------------
+    rdma_en2        	8096a9d9edbaac05
+    rdma_en3        	8196a9d9edbaac05
+    rdma_en5        	8396a9d9edbaac05
+    rdma_en4        	8296a9d9edbaac05
+    rdma_en6        	8496a9d9edbaac05
+    rdma_en7        	8596a9d9edbaac05
+
+Defining a Mesh
+^^^^^^^^^^^^^^^
+
+The JACCL backend supports only fully connected topologies. Namely, there needs
+to be a thunderbolt cable connecting all pairs of Macs directly. For example, in
+the following topology visualizations, the left one is valid because there is a
+connection from any node to any other node, while for the one on the right M3
+Ultra 1 is not connected to M3 Ultra 2.
+
+.. raw:: html
+
+   <div style="display: flex; text-align: center; align-items: end; font-size: 80%;">
+     <div>
+       <img src="/_static/distributed/m3-ultra-mesh.png" alt="M3 Ultra thunderbolt mesh" style="width: 55%">
+       <p>Fully connected mesh of four M3 Ultra.</p>
+     </div>
+     <div>
+       <img src="/_static/distributed/m3-ultra-mesh-broken.png" alt="M3 Ultra broken thunderbolt mesh" style="width: 55%">
+       <p>Not a valid mesh (M3 Ultra 1 is not connected to M3 Ultra 2).</p>
+     </div>
+   </div>
+
+Similar to the ring backend, the easiest way to use JACCL with MLX is to write
+a JSON hostfile that will be used by ``mlx.launch``. The hostfile needs to contain
+
+- Hostnames to use for launching scripts via ssh
+- An IP for rank 0 that is reachable by all nodes
+- A list of rdma devices that connect each node to each other node
+
+The following JSON defines the valid 4-node mesh from the image above.
+
+.. code-block:: json
+
+    [
+        {
+            "ssh": "m3-ultra-1",
+            "ips": ["123.123.123.1"],
+            "rdma": [null, "rdma_en5", "rdma_en4", "rdma_en3"]
+        },
+        {
+            "ssh": "m3-ultra-2",
+            "ips": [],
+            "rdma": ["rdma_en5", null, "rdma_en3", "rdma_en4"]
+        },
+        {
+            "ssh": "m3-ultra-3",
+            "ips": [],
+            "rdma": ["rdma_en4", "rdma_en3", null, "rdma_en5"]
+        },
+        {
+            "ssh": "m3-ultra-4",
+            "ips": [],
+            "rdma": ["rdma_en3", "rdma_en4", "rdma_en5", null]
+        }
+    ]
+
+Even though TCP/IP is not used when communicating with Thunderbolt RDMA,
+disabling the thunderbolt bridge is still required as well as setting up
+isolated local networks for each thunderbolt connection.
+
+All of the above can be done instead via ``mlx.distributed_config``. This helper
+script will
+
+- ssh into each node
+- extract the thunderbolt connectivity
+- check for a valid mesh
+- provide the commands to configure each node (or run them if sudo is available)
+- generate the hostfile to be used with ``mlx.launch``
+
+Putting it All Together
+^^^^^^^^^^^^^^^^^^^^^^^^
+
+For example launching a distributed MLX script that uses JACCL is fairly simple
+if the nodes are reachable via ssh and have password-less sudo.
+
+First, connect all the thunderbolt cables. Then we can verify the connections
+by using the ``mlx.distributed_config`` script to visualize them.
+
+.. code-block::
+
+   mlx.distributed_config --verbose \
+        --hosts m3-ultra-1,m3-ultra-2,m3-ultra-3,m3-ultra-4 \
+        --over thunderbolt --dot | dot -Tpng | open -f -a Preview
+
+After making sure that everything looks right we can auto-configure the nodes
+and save the hostfile to ``m3-ultra-jaccl.json`` by running:
+
+.. code-block::
+
+   mlx.distributed_config --verbose \
+        --hosts m3-ultra-1,m3-ultra-2,m3-ultra-3,m3-ultra-4 \
+        --over thunderbolt --backend jaccl \
+        --auto-setup --output m3-ultra-jaccl.json
+
+And now we are ready to run a distributed MLX script such as distributed inference
+of a gigantic model using MLX-LM.
+
+.. code-block::
+
+   mlx.launch --verbose --backend jaccl --hostfile m3-ultra-jaccl.json \
+        --env MLX_METAL_FAST_SYNCH=1 -- \  # <--- important
+        /path/to/remote/python -m mlx_lm chat --model mlx-community/DeepSeek-V3.2-8bit --shard
+
+.. note::
+
+   Defining the environment variable ``MLX_METAL_FAST_SYNCH=1`` enables a
+   different, faster way of synchronizing between the GPU and the CPU. It is
+   not specific to the JACCL backend and can be used in all cases where the CPU
+   and GPU need to collaborate for some computation and is pretty critical for
+   low-latency communication since the communication is done by the CPU.
+
+.. _nccl_section:
+
+Getting Started with NCCL
+-------------------------
+
+MLX on CUDA environments ships with the ability to talk to `NCCL
+<https://developer.nvidia.com/nccl>`_ which is a high-performance collective
+communication library that supports both multi-gpu and multi-node setups.
+
+For CUDA environments, NCCL is the default backend for ``mlx.launch`` and all
+it takes to run a distributed job is
+
+.. code-block::
+
+   mlx.launch -n 8 test.py
+
+   # perfect for interactive scripts
+   mlx.launch -n 8 python -m mlx_lm chat --model my-model --shard
+
+You can also use ``mlx.launch`` to ssh to a remote node and launch a script
+with the same ease
+
+.. code-block::
+
+   mlx.launch --hosts my-cuda-node -n 8 test.py
+
+In many cases you may not want to use ``mlx.launch`` with the NCCL backend
+because the cluster scheduler will be the one launching the processes. You can
+:ref:`see which environment variables need to be defined <no_mlx_launch>` in
+order for the MLX NCCL backend to be initialized correctly.
+
+.. _mpi_section:
 
 Getting Started with MPI
 ------------------------
 
-MLX already comes with the ability to "talk" to MPI if it is installed on the
+MLX already comes with the ability to "talk" to `MPI
-machine. Launching distributed MLX programs that use MPI can be done with
+<https://en.wikipedia.org/wiki/Message_Passing_Interface>`_ if it is installed
-``mpirun`` as expected. However, in the following examples we will be using
+on the machine. Launching distributed MLX programs that use MPI can be done
-``mlx.launch --backend mpi`` which takes care of some nuisances such as setting
+with ``mpirun`` as expected. However, in the following examples we will be
-absolute paths for the ``mpirun`` executable and the ``libmpi.dyld`` shared
+using ``mlx.launch --backend mpi`` which takes care of some nuisances such as
-library.
+setting absolute paths for the ``mpirun`` executable and the ``libmpi.dyld``
+shared library.
 
 The simplest possible usage is the following which, assuming the minimal
 example in the beginning of this page, should result in:
@@ -269,78 +535,116 @@ Force MPI to use the most performant network interface by setting ``--mca
 btl_tcp_if_include <iface>`` where ``<iface>`` should be the interface you want
 to use.
 
-Getting Started with Ring
+.. _no_mlx_launch:
--------------------------
 
-The ring backend does not depend on any third party library so it is always
+Distributed Without ``mlx.launch``
-available. It uses TCP sockets so the nodes need to be reachable via a network.
+----------------------------------
-As the name suggests the nodes are connected in a ring which means that rank 1
-can only communicate with rank 0 and rank 2, rank 2 only with rank 1 and rank 3
-and so on and so forth. As a result :func:`send` and :func:`recv` with
-arbitrary sender and receiver is not supported in the ring backend.
 
-Defining a Ring
+None of the implementations of the distributed backends require launching with
-^^^^^^^^^^^^^^^
+``mlx.launch``. The script simply connects to each host. Starts a process per
+rank and sets up the necessary environment variables before delegating to your
+MLX script. See the :doc:`dedicated documentation page <launching_distributed>`
+for more details.
 
-The easiest way to define and use a ring is via a JSON hostfile and the
+For many use-cases this will be the easiest way to perform distributed
-``mlx.launch`` :doc:`helper script <launching_distributed>`. For each node one
+computations in MLX. However, there may be reasons that you cannot or should
-defines a hostname to ssh into to run commands on this node and one or more IPs
+not use ``mlx.launch``. A common such case is the use of a scheduler that
-that this node will listen to for connections.
+starts all the processes for you on machines undetermined at the time of
+scheduling the job.
 
-For example the hostfile below defines a 4 node ring. ``hostname1`` will be
+Below we list the environment variables required to use each backend.
-rank 0, ``hostname2`` rank 1 etc.
 
-.. code:: json
+Ring
+^^^^^^
 
-    [
+**MLX_RANK** should contain a single 0-based integer that defines the rank of
-        {"ssh": "hostname1", "ips": ["123.123.123.1"]},
+the process.
-        {"ssh": "hostname2", "ips": ["123.123.123.2"]},
-        {"ssh": "hostname3", "ips": ["123.123.123.3"]},
-        {"ssh": "hostname4", "ips": ["123.123.123.4"]}
-    ]
 
-Running ``mlx.launch --hostfile ring-4.json my_script.py`` will ssh into each
+**MLX_HOSTFILE** should contain the path to a json file that contains IPs and
-node, run the script which will listen for connections in each of the provided
+ports for each rank to listen to, something like the following:
-IPs. Specifically, ``hostname1`` will connect to ``123.123.123.2`` and accept a
-connection from ``123.123.123.4`` and so on and so forth.
 
-Thunderbolt Ring
+.. code-block:: json
-^^^^^^^^^^^^^^^^
 
-Although the ring backend can have benefits over MPI even for Ethernet, its
+   [
-main purpose is to use Thunderbolt rings for higher bandwidth communication.
+     ["123.123.1.1:5000", "123.123.1.2:5000"],
-Setting up such thunderbolt rings can be done manually, but is a relatively
+     ["123.123.2.1:5000", "123.123.2.2:5000"],
-tedious process. To simplify this, we provide the utility ``mlx.distributed_config``.
+     ["123.123.3.1:5000", "123.123.3.2:5000"],
+     ["123.123.4.1:5000", "123.123.4.2:5000"]
+   ]
 
-To use ``mlx.distributed_config`` your computers need to be accessible by ssh via
+**MLX_RING_VERBOSE** is optional and if set to 1 it enables some more logging
-Ethernet or Wi-Fi. Subsequently, connect them via thunderbolt cables and then call the
+from the distributed backend.
-utility as follows:
 
-.. code:: shell
+JACCL
+^^^^^
 
-   mlx.distributed_config --verbose --hosts host1,host2,host3,host4
+**MLX_RANK** should contain a single 0-based integer that defines the rank of
+the process.
 
-By default the script will attempt to discover the thunderbolt ring and provide
+**MLX_JACCL_COORDINATOR** should contain the IP and port that rank 0 can listen
-you with the commands to configure each node as well as the ``hostfile.json``
+to all the other ranks connect to in order to establish the RDMA connections.
-to use with ``mlx.launch``. If password-less ``sudo`` is available on the nodes
-then ``--auto-setup`` can be used to configure them automatically.
 
-To validate your connection without configuring anything
+**MLX_IBV_DEVICES** should contain the path to a json file that contains the
-``mlx.distributed_config`` can also plot the ring using DOT format.
+ibverbs device names that connect each node to each other node, something like
+the following:
 
-.. code:: shell
+.. code-block:: json
 
-   mlx.distributed_config --verbose --hosts host1,host2,host3,host4 --dot >ring.dot
+   [
-   dot -Tpng ring.dot >ring.png
+      [null, "rdma_en5", "rdma_en4", "rdma_en3"],
-   open ring.png
+      ["rdma_en5", null, "rdma_en3", "rdma_en4"],
+      ["rdma_en4", "rdma_en3", null, "rdma_en5"],
+      ["rdma_en3", "rdma_en4", "rdma_en5", null]
+   ]
 
-If you want to go through the process manually, the steps are as follows:
 
-* Disable the thunderbolt bridge interface
+NCCL
-* For the cable connecting rank ``i`` to rank ``i + 1`` find the interfaces
+^^^^^
-  corresponding to that cable in nodes ``i`` and ``i + 1``.
+
-* Set up a unique subnetwork connecting the two nodes for the corresponding
+**MLX_RANK** should contain a single 0-based integer that defines the rank of
-  interfaces. For instance if the cable corresponds to ``en2`` on node ``i``
+the process.
-  and ``en2`` also on node ``i + 1`` then we may assign IPs ``192.168.0.1`` and
+
-  ``192.168.0.2`` respectively to the two nodes. For more details you can see
+**MLX_WORLD_SIZE** should contain the total number of processes that will be
-  the commands prepared by the utility script.
+launched.
+
+**NCCL_HOST_IP** and **NCCL_PORT** should contain the IP and port that all
+hosts can connect to to establish the NCCL communication.
+
+**CUDA_VISIBLE_DEVICES** should contain the local index of the gpu that
+corresponds to this process.
+
+Of course any `other environment variable
+<https://docs.nvidia.com/deeplearning/nccl/user-guide/docs/env.html>`_ that is
+used by NCCL can be set.
+
+.. _tips_and_tricks:
+
+Tips and Tricks
+----------------
+
+This is a small collection of tips to help you utilize better the distributed
+communication capabilities of MLX.
+
+- *Test locally first.*
+
+  You can use the pattern ``mlx.launch -n2 -- my_script.py`` to run a small
+  scale test on a single node first.
+
+- *Batch your communication.*
+
+  As described in the :ref:`training example <training_example>`, performing a
+  lot of small communication can hurt performance. Copy the approach of
+  :func:`mlx.nn.average_gradients` to gather many small communications in a
+  single large one.
+
+- *Visualize the connectivity.*
+
+  Use ``mlx.distributed_config --hosts h1,h2,h3 --over thunderbolt --dot`` to
+  visualize the connnections and make sure that the cables are connected
+  correctly. See the :ref:`JACCL section <jaccl_section>` for examples.
+
+- *Use the debugger.*
+
+  ``mlx.launch`` is meant for interactive use. It broadcasts stdin to all
+  processes and gathers stdout from all processes. This makes using ``pdb`` a
+  breeze.

docs/src/usage/launching_distributed.rst

@@ -7,13 +7,106 @@ Launching Distributed Programs
 
 .. currentmodule:: mlx.core.distributed
 
-Installing the MLX python package provides a helper script ``mlx.launch`` that
+Installing the MLX python package provides two utilities to help you configure
-can be used to run python scripts distributed on several nodes. It allows
+your Macs for distributed computation and also launch distributed programs on
-launching using either the MPI backend or the ring backend. See the
+multiple nodes or with many processes in a single node. These utilities are aptly named
-:doc:`distributed docs <distributed>` for the different backends.
 
-Usage
+- ``mlx.launch``
------
+- ``mlx.distributed_config``
+
+See the :doc:`distributed docs <distributed>` for an introduction and
+getting-started guides to the various backends.
+
+``mlx.distributed_config`` 
+---------------------------
+
+Unless you are launching distributed jobs locally for development or multi-gpu
+CUDA environments, then you have several Macs that you need to configure for
+distributed communication with MLX.
+
+``mlx.distributed_config`` aims to automate the process of configuring the
+network interfaces (especially for communication over thunderbolt) and also
+creating the hostfile to be used with ``mlx.launch``.
+
+We will analyse 3 cases of using ``mlx.distributed_config``
+
+1. RDMA over thunderbolt using JACCL
+2. TCP/IP over thunderbolt using the ring backend
+3. TCP/IP over ethernet using the ring backend
+
+JACCL
+^^^^^^^
+
+After following :ref:`the steps to enable RDMA <jaccl_section>` you can run the
+following command to configure the nodes and create the hostfile.
+
+.. code-block::
+
+   mlx.distributed_config --verbose --backend jaccl \
+        --hosts m3-ultra-1,m3-ultra-2,m3-ultra-3,m3-ultra-4 --over thunderbolt \
+        --auto-setup --output m3-ultra-jaccl.json
+
+Let's walk through the steps that the script takes to configure the nodes.
+
+1. Ssh to all nodes to verify that they are reachable
+2. Extract the thunderbolt connectivity. Namely run commands on each node to
+   calculate which node is connected to which other node.
+3. Verify that we have a valid fully connected mesh
+4. Check that RDMA is enabled
+5. Extract the ethernet IP from interface en0
+6. Disable the thunderbolt bridge and set up peer to peer networks for each
+   thunderbolt cable
+7. Write the hostfile
+
+Knowing the above steps allows you to manually configure the nodes but also
+debug any configuration issue. For instance changing the Ethernet IP to a
+different interface directly in the config is possible (as long as it is
+reachable from all nodes).
+
+The ``--auto-setup`` argument requires password-less sudo on each node. If it
+isn't available then the configuration script will print commands to be run on
+each node.
+
+Ring over thunderbolt
+^^^^^^^^^^^^^^^^^^^^^
+
+Setting up a ring backend over thunderbolt only requires changing the
+``--backend`` from ``jaccl`` to ``ring``.
+
+The steps are very similar with the main difference being that instead of
+verifying that the nodes are fully connected, the script attempts to identify a
+ring topology (or multiple rings).
+
+Ring over Ethernet
+^^^^^^^^^^^^^^^^^^
+
+Configuring the ring backend over ethernet doesn't require setting up network
+interface and as such it simply extracts the ``en0`` IP from each node and
+writes the hostfile.
+
+Debugging cable connections
+^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+``mlx.distributed_config`` can help you debug the connectivity of your nodes
+over thunderbolt by exporting a graph of the connections.
+
+Running
+
+.. code-block::
+
+   mlx.distributed_config --verbose \
+        --hosts host1,host2,host3,host4 \
+        --over thunderbolt --dot
+
+will export a `GraphViz <https://graphviz.org>`_ representation of the
+connections between the nodes which makes it very easy to figure out which
+cable is not connected correctly.
+
+See :ref:`the JACCL section <jaccl_section>` for an example.
+
+
+``mlx.launch``
+--------------
 
 The minimal usage example of ``mlx.launch`` is simply
 
@@ -33,6 +126,10 @@ the rest if one of them fails unexpectedly or if ``mlx.launch`` is terminated.
 It also takes care of forwarding the output of each remote process to stdout
 and stderr respectively.
 
+Importantly, it also broadcasts stdin to each process which enables interactive
+programs to work in distributed mode as well as debugging using the interactive
+debugger.
+
 Providing Hosts
 ^^^^^^^^^^^^^^^^
 
@@ -63,10 +160,62 @@ host and on the same path. A good checklist to debug errors is the following:
   ``mlx.launch --print-python`` to see what that path is.
 * the script you want to run is available on all hosts at the same path
 
+If you are launching from a node with a completely different setup than the
+nodes that the program will run on, you can specify ``--no-verify-script`` so
+that ``mlx.launch`` does not attempt to verify that the executable and script
+exist locally before launching the distributed job.
+
+.. _ring_specifics:
+
+Ring Specifics
+^^^^^^^^^^^^^^
+
+The :ref:`ring <ring_section>` backend, which is also the default
+backend, can be explicitly selected with the argument ``--backend ring``. The
+ring backend has some specific requirements and arguments that are different to
+other backends:
+
+* The argument ``--hosts`` only accepts IPs and not hostnames. If we need to
+  ssh to a hostname that does not correspond to the IP we want to bind to we
+  have to provide a hostfile.
+* ``--starting-port`` defines the port to bind to on the remote hosts.
+  Specifically rank 0 for the first IP will use this port and each subsequent
+  IP or rank will add 1 to this port.
+* ``--connections-per-ip`` allows us to increase the number of connections
+  between neighboring nodes. This corresponds to ``--mca btl_tcp_links 2`` for
+  ``mpirun``.
+
+.. _jaccl_specifics:
+
+JACCL Specifics
+^^^^^^^^^^^^^^^^
+
+The :ref:`JACCL <jaccl_section>` backend can be selected with the argument
+``--backend jaccl``. A hostfile is necessary to launch with this backend
+because it needs to contain the RDMA devices connecting each node to each other
+node.
+
+NCCL Specifics
+^^^^^^^^^^^^^^
+
+The :ref:`NCCL <nccl_section>` backend is the default backend for CUDA
+environments. When launching from a Mac to a Linux machine with CUDA then the
+backend should be selected using ``--backend nccl``.
+
+The ``--repeat-hosts, -n`` argument should be used to launch multi-node and
+multi-gpu jobs. For instance
+
+.. code-block::
+
+   mlx.launch --backend nccl --hosts linux-1,linux-2 -n 8 --no-verify-script -- ./my-job.sh
+
+will attempt to launch 16 processes, 8 on each node that will all run
+``my-job.sh``.
+
 .. _mpi_specifics:
 
 MPI Specifics
--------------
+^^^^^^^^^^^^^
 
 One can use MPI by passing ``--backend mpi`` to ``mlx.launch``. In that case,
 ``mlx.launch`` is a thin wrapper over ``mpirun``. Moreover,
@@ -83,23 +232,3 @@ to choose a specific interface for the byte-transfer-layer of MPI we can call
 .. code:: shell
 
     mlx.launch --backend mpi --mpi-arg '--mca btl_tcp_if_include en0' --hostfile hosts.json my_script.py
-
-
-.. _ring_specifics:
-
-Ring Specifics
---------------
-
-The ring backend, which is also the default backend, can be explicitly selected
-with the argument ``--backend ring``. The ring backend has some specific
-requirements and arguments that are different to MPI:
-
-* The argument ``--hosts`` only accepts IPs and not hostnames. If we need to
-  ssh to a hostname that does not correspond to the IP we want to bind to we
-  have to provide a hostfile.
-* ``--starting-port`` defines the port to bind to on the remote hosts.
-  Specifically rank 0 for the first IP will use this port and each subsequent
-  IP or rank will add 1 to this port.
-* ``--connections-per-ip`` allows us to increase the number of connections
-  between neighboring nodes. This corresponds to ``--mca btl_tcp_links 2`` for
-  ``mpirun``.

mlx/CMakeLists.txt

@@ -1,7 +1,6 @@
 target_sources(
   mlx
-  PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/allocator.cpp
+  PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/array.cpp
-          ${CMAKE_CURRENT_SOURCE_DIR}/array.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/compile.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/device.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/dtype.cpp

mlx/allocator.cpp

@@ -1,24 +0,0 @@
-// Copyright © 2023 Apple Inc.
-
-#include <cstdlib>
-#include <sstream>
-
-#include "mlx/allocator.h"
-
-namespace mlx::core::allocator {
-
-Buffer malloc(size_t size) {
-  auto buffer = allocator().malloc(size);
-  if (size && !buffer.ptr()) {
-    std::ostringstream msg;
-    msg << "[malloc] Unable to allocate " << size << " bytes.";
-    throw std::runtime_error(msg.str());
-  }
-  return buffer;
-}
-
-void free(Buffer buffer) {
-  allocator().free(buffer);
-}
-
-} // namespace mlx::core::allocator

mlx/allocator.h

@@ -28,16 +28,16 @@ class Buffer {
   };
 };
 
-Buffer malloc(size_t size);
-
-void free(Buffer buffer);
-
 class Allocator {
   /** Abstract base class for a memory allocator. */
  public:
   virtual Buffer malloc(size_t size) = 0;
   virtual void free(Buffer buffer) = 0;
   virtual size_t size(Buffer buffer) const = 0;
+  virtual Buffer make_buffer(void* ptr, size_t size) {
+    return Buffer{nullptr};
+  };
+  virtual void release(Buffer buffer) {}
 
   Allocator() = default;
   Allocator(const Allocator& other) = delete;
@@ -49,4 +49,25 @@ class Allocator {
 
 Allocator& allocator();
 
+inline Buffer malloc(size_t size) {
+  return allocator().malloc(size);
+}
+
+inline void free(Buffer buffer) {
+  allocator().free(buffer);
+}
+
+// Make a Buffer from a raw pointer of the given size without a copy.  If a
+// no-copy conversion is not possible then the returned buffer.ptr() will be
+// nullptr. Any buffer created with this function must be released with
+// release(buffer)
+inline Buffer make_buffer(void* ptr, size_t size) {
+  return allocator().make_buffer(ptr, size);
+};
+
+// Release a buffer from the allocator made with make_buffer
+inline void release(Buffer buffer) {
+  allocator().release(buffer);
+}
+
 } // namespace mlx::core::allocator

mlx/array.cpp

@@ -82,6 +82,28 @@ array::array(std::initializer_list<int> data, Dtype dtype)
   init(data.begin());
 }
 
+array::array(
+    void* data,
+    Shape shape,
+    Dtype dtype,
+    const std::function<void(void*)>& deleter)
+    : array_desc_(std::make_shared<ArrayDesc>(std::move(shape), dtype)) {
+  auto buffer = allocator::make_buffer(data, nbytes());
+  if (buffer.ptr() == nullptr) {
+    set_data(allocator::malloc(nbytes()));
+    auto ptr = static_cast<char*>(data);
+    std::copy(ptr, ptr + nbytes(), this->data<char>());
+    deleter(data);
+  } else {
+    auto wrapped_deleter = [deleter](allocator::Buffer buffer) {
+      auto ptr = buffer.ptr();
+      allocator::release(buffer);
+      return deleter(ptr);
+    };
+    set_data(buffer, std::move(wrapped_deleter));
+  }
+}
+
 /* Build an array from a shared buffer */
 array::array(allocator::Buffer data, Shape shape, Dtype dtype, Deleter deleter)
     : array_desc_(std::make_shared<ArrayDesc>(std::move(shape), dtype)) {

mlx/array.h

@@ -57,6 +57,16 @@ class array {
       Shape shape,
       Dtype dtype = TypeToDtype<T>());
 
+  /* Build an array from a raw pointer. The constructor will attempt to use the
+   * input data without a copy. The deleter will be called when the array no
+   * longer needs the underlying memory - after the array is destroyed in the
+   * no-copy case and after the copy otherwise. */
+  explicit array(
+      void* data,
+      Shape shape,
+      Dtype dtype,
+      const std::function<void(void*)>& deleter);
+
   /* Build an array from a buffer */
   explicit array(
       allocator::Buffer data,

mlx/backend/cuda/allocator.cpp

@@ -20,6 +20,19 @@ constexpr int page_size = 16384;
 // Any allocations smaller than this will try to use the small pool
 constexpr int small_block_size = 8;
 
+#if CUDART_VERSION >= 13000
+inline cudaMemLocation cuda_mem_loc(int i) {
+  cudaMemLocation loc;
+  loc.type = cudaMemLocationTypeDevice;
+  loc.id = i;
+  return loc;
+}
+#else
+inline int cuda_mem_loc(int i) {
+  return i;
+}
+#endif // CUDART_VERSION >= 13000
+
 // The small pool size in bytes. This should be a multiple of the host page
 // size and small_block_size.
 constexpr int small_pool_size = 4 * page_size;
@@ -35,13 +48,7 @@ SmallSizePool::SmallSizePool() {
   int device_count = 0;
   CHECK_CUDA_ERROR(cudaGetDeviceCount(&device_count));
   for (int i = 0; i < device_count; ++i) {
-#if CUDART_VERSION >= 13000
+    auto loc = cuda_mem_loc(i);
-    cudaMemLocation loc;
-    loc.type = cudaMemLocationTypeDevice;
-    loc.id = i;
-#else
-    int loc = i;
-#endif // CUDART_VERSION >= 13000
     CHECK_CUDA_ERROR(
         cudaMemAdvise(data_, small_pool_size, cudaMemAdviseSetAccessedBy, loc));
   }
@@ -90,9 +97,10 @@ CudaAllocator::CudaAllocator()
           page_size,
           [](CudaBuffer* buf) { return buf->size; },
           [this](CudaBuffer* buf) { cuda_free(buf); }) {
-  size_t free, total;
+  size_t free;
-  CHECK_CUDA_ERROR(cudaMemGetInfo(&free, &total));
+  CHECK_CUDA_ERROR(cudaMemGetInfo(&free, &total_memory_));
-  memory_limit_ = total * 0.9;
+  memory_limit_ = total_memory_ * 0.95;
+  free_limit_ = total_memory_ - memory_limit_;
   max_pool_size_ = memory_limit_;
 
   int device_count = 0;
@@ -104,6 +112,10 @@ CudaAllocator::CudaAllocator()
     cudaStream_t s;
     CHECK_CUDA_ERROR(cudaStreamCreateWithFlags(&s, cudaStreamNonBlocking));
     free_streams_.push_back(s);
+
+    cudaMemPool_t mem_pool;
+    CHECK_CUDA_ERROR(cudaDeviceGetDefaultMemPool(&mem_pool, i));
+    mem_pools_.push_back(mem_pool);
   }
   CHECK_CUDA_ERROR(cudaSetDevice(curr));
 }
@@ -154,23 +166,35 @@ CudaAllocator::malloc_async(size_t size, int device, cudaStream_t stream) {
     }
     lock.unlock();
     if (!buf) {
-      cudaError_t err;
       void* data = nullptr;
       if (device == -1) {
-        err = cudaMallocManaged(&data, size);
+        CHECK_CUDA_ERROR(cudaMallocManaged(&data, size));
       } else {
-        err = cudaMallocAsync(&data, size, stream);
+        CHECK_CUDA_ERROR(cudaMallocAsync(&data, size, stream));
-      }
-      if (err != cudaSuccess && err != cudaErrorMemoryAllocation) {
-        throw std::runtime_error(fmt::format(
-            "cudaMallocManaged failed: {}.", cudaGetErrorString(err)));
       }
       if (!data) {
-        return Buffer{nullptr};
+        std::ostringstream msg;
+        msg << "[malloc] Unable to allocate " << size << " bytes.";
+        throw std::runtime_error(msg.str());
       }
       buf = new CudaBuffer{data, size, device};
     }
     lock.lock();
+
+    // If any cuda memory pool has too much reserved memory, clear some
+    // memory from the cache. This prevents graph / kernel execution failing
+    // from OOM
+    if (get_cache_memory() > 0) {
+      for (auto p : mem_pools_) {
+        size_t used = 0;
+        CHECK_CUDA_ERROR(cudaMemPoolGetAttribute(
+            p, cudaMemPoolAttrReservedMemCurrent, &used));
+        if (used > (total_memory_ - free_limit_)) {
+          buffer_cache_.release_cached_buffers(free_limit_);
+          break;
+        }
+      }
+    }
   }
   active_memory_ += buf->size;
   peak_memory_ = std::max(active_memory_, peak_memory_);

mlx/backend/cuda/allocator.h

@@ -71,11 +71,14 @@ class CudaAllocator : public allocator::Allocator {
 
   std::mutex mutex_;
   size_t memory_limit_;
+  size_t free_limit_;
+  size_t total_memory_;
   size_t max_pool_size_;
   BufferCache<CudaBuffer> buffer_cache_;
   size_t active_memory_{0};
   size_t peak_memory_{0};
   std::vector<cudaStream_t> free_streams_;
+  std::vector<cudaMemPool_t> mem_pools_;
   SmallSizePool scalar_pool_;
 };
 

mlx/backend/cuda/copy/copy_general_input.cu

@@ -95,11 +95,14 @@ void copy_general_input(
             const InType* in_ptr = gpu_ptr<InType>(in) + offset_in;
             OutType* out_ptr = gpu_ptr<OutType>(out) + offset_out;
             int ndim = shape.size();
-            int work_per_thread = 1;
+
+            int work_per_thread = 8;
             auto dim0 = ndim > 0 ? shape.back() : 1;
             auto rest = out.size() / dim0;
-            if (dim0 >= 4) {
+            if (dim0 >= 4 && dim0 < 8) {
               work_per_thread = 4;
+            } else if (dim0 < 4) {
+              work_per_thread = 1;
             }
             dim0 = (dim0 + work_per_thread - 1) / work_per_thread;
             auto block_dims = get_block_dims(dim0, rest, 1);
@@ -110,7 +113,10 @@ void copy_general_input(
               dispatch_1_2_3(ndim, [&](auto dims_constant) {
                 auto kernel =
                     cu::copy_g_nd<InType, OutType, IdxT, dims_constant(), 1>;
-                if (work_per_thread == 4) {
+                if (work_per_thread == 8) {
+                  kernel =
+                      cu::copy_g_nd<InType, OutType, IdxT, dims_constant(), 8>;
+                } else if (work_per_thread == 4) {
                   kernel =
                       cu::copy_g_nd<InType, OutType, IdxT, dims_constant(), 4>;
                 }
@@ -127,7 +133,9 @@ void copy_general_input(
               });
             } else { // ndim >= 4
               auto kernel = cu::copy_g<InType, OutType, IdxT, 1>;
-              if (work_per_thread == 4) {
+              if (work_per_thread == 8) {
+                kernel = cu::copy_g<InType, OutType, IdxT, 8>;
+              } else if (work_per_thread == 4) {
                 kernel = cu::copy_g<InType, OutType, IdxT, 4>;
               }
               encoder.add_kernel_node(

mlx/backend/cuda/device.cpp

@@ -318,46 +318,52 @@ void CommandEncoder::add_kernel_node(const CUDA_KERNEL_NODE_PARAMS& params) {
   insert_graph_dependencies(GraphNode{node, "K"});
 }
 
-bool is_graph_updatable(cudaGraph_t graph, int& cluster_dim_x) {
+std::pair<std::string, bool> subgraph_to_key(cudaGraph_t graph) {
-  // CUDA graphs do not get updated correctly if a kernel node getting updated
+  // Constructs a key representing the nodes of a sub-graph.
-  // has a different cluster shape than the node it's being updated with.
+  // Also checks if the sub-graph is updatable as CUDA graphs do not get
+  // updated correctly if a kernel node getting updated has a different cluster
+  // shape than the node it's being updated with.
+  std::string key = "(";
   size_t num_nodes = 0;
   CHECK_CUDA_ERROR(cudaGraphGetNodes(graph, nullptr, &num_nodes));
   if (num_nodes == 0) {
-    return true;
+    return {key + ")", true};
   }
-
+  bool is_updatable = true;
   std::vector<cudaGraphNode_t> nodes(num_nodes);
   CHECK_CUDA_ERROR(cudaGraphGetNodes(graph, nodes.data(), &num_nodes));
   for (const auto& node : nodes) {
+    if (!is_updatable) {
+      break;
+    }
     cudaGraphNodeType type;
     CHECK_CUDA_ERROR(cudaGraphNodeGetType(node, &type));
     if (type == cudaGraphNodeTypeGraph) {
       // Try to be updatable for a structure like graph -> graph -> kernel
-      if (num_nodes > 1) {
-        return false;
-      }
       cudaGraph_t child;
       CHECK_CUDA_ERROR(cudaGraphChildGraphNodeGetGraph(node, &child));
-      return is_graph_updatable(child, cluster_dim_x);
+      auto [subkey, sub_is_updatable] = subgraph_to_key(child);
+      is_updatable &= sub_is_updatable;
+      key += subkey;
+    } else if (type == cudaGraphNodeTypeMemset) {
+      key += "M";
     } else if (type != cudaGraphNodeTypeKernel) {
-      return false;
+      is_updatable = false;
     } else {
       cudaLaunchAttributeValue cluster_dim;
       CHECK_CUDA_ERROR(cudaGraphKernelNodeGetAttribute(
           node, cudaLaunchAttributeClusterDimension, &cluster_dim));
-      // Only dim.x can be greater than 1
+      // Only allow dim.x to be greater than 1
       if (cluster_dim.clusterDim.y > 1 || cluster_dim.clusterDim.z > 1) {
-        return false;
+        is_updatable = false;
+      } else {
+        key += "K";
+        key += std::to_string(cluster_dim.clusterDim.x);
       }
-      // Only one child node allowed when subgraph uses clusters
-      if (cluster_dim.clusterDim.x > 0 && num_nodes > 1) {
-        return false;
-      }
-      cluster_dim_x = cluster_dim.clusterDim.x;
     }
   }
-  return true;
+  key += ")";
+  return {key, is_updatable};
 }
 
 void CommandEncoder::add_graph_node(cudaGraph_t child) {
@@ -370,11 +376,10 @@ void CommandEncoder::add_graph_node(cudaGraph_t child) {
     return;
   }
   cudaGraphNode_t node;
-  int cluster_dim_x = 0;
+  auto [sub_graph_key, is_updatable] = subgraph_to_key(child);
-  is_graph_updatable_ &= is_graph_updatable(child, cluster_dim_x);
+  is_graph_updatable_ &= is_updatable;
   CHECK_CUDA_ERROR(cudaGraphAddChildGraphNode(&node, graph_, NULL, 0, child));
-  insert_graph_dependencies(
+  insert_graph_dependencies(GraphNode{node, sub_graph_key});
-      GraphNode{node, "G" + std::to_string(cluster_dim_x)});
 }
 
 bool CommandEncoder::needs_commit() {

mlx/backend/cuda/device.h

@@ -106,7 +106,7 @@ class CommandEncoder {
     cudaGraphNode_t node;
     // K = kernel
     // E = empty
-    // G* = subgraph (with metadata)
+    // () = subgraph (with metadata)
     // Symbols ':', '-' are reserved as separators
     std::string node_type;
     std::string id;

mlx/backend/cuda/reduce/col_reduce.cu

@@ -89,9 +89,13 @@ template <
     int NDIM,
     int BM,
     int BN,
-    int N_READS = 4>
+    int N_READS = 4,
-__global__ void
+    int BLOCKS = 1>
-col_reduce_looped(T* in, U* out, const __grid_constant__ ColReduceArgs args) {
+__global__ void col_reduce_looped(
+    T* in,
+    U* out,
+    const __grid_constant__ ColReduceArgs args,
+    int64_t out_size) {
   auto grid = cg::this_grid();
   auto block = cg::this_thread_block();
   auto warp = cg::tiled_partition<WARP_SIZE>(block);
@@ -102,6 +106,8 @@ col_reduce_looped(T* in, U* out, const __grid_constant__ ColReduceArgs args) {
   size_t tile_idx = grid.block_rank();
   size_t tile_x = tile_idx % ((args.reduction_stride + BN - 1) / BN);
   size_t tile_y = tile_idx / ((args.reduction_stride + BN - 1) / BN);
+  size_t tile_out = tile_y / out_size;
+  tile_y = tile_y % out_size;
 
   // Compute the indices for the thread within the tile
   short thread_x = block.thread_rank() % threads_per_row;
@@ -118,12 +124,23 @@ col_reduce_looped(T* in, U* out, const __grid_constant__ ColReduceArgs args) {
     totals[i] = ReduceInit<Op, T>::value();
   }
 
-  LoopedElemToLoc<NDIM, (NDIM > 2)> loop(args.reduce_ndim);
-  loop.next(thread_y, args.reduce_shape.data(), args.reduce_strides.data());
   size_t total = args.non_col_reductions * args.reduction_size;
+  size_t per_block, start, end;
+  if constexpr (BLOCKS > 1) {
+    per_block = (total + BLOCKS - 1) / BLOCKS;
+    start = tile_out * per_block + thread_y;
+    end = min((tile_out + 1) * per_block, total);
+  } else {
+    per_block = total;
+    start = thread_y;
+    end = total;
+  }
+
+  LoopedElemToLoc<NDIM, (NDIM > 2)> loop(args.reduce_ndim);
+  loop.next(start, args.reduce_shape.data(), args.reduce_strides.data());
   if (tile_x * BN + BN <= args.reduction_stride) {
     if (args.reduction_stride % N_READS == 0) {
-      for (size_t r = thread_y; r < total; r += BM) {
+      for (size_t r = start; r < end; r += BM) {
         T vals[N_READS];
         cub::LoadDirectBlockedVectorized(thread_x, in + loop.location(), vals);
         for (int i = 0; i < N_READS; i++) {
@@ -132,7 +149,7 @@ col_reduce_looped(T* in, U* out, const __grid_constant__ ColReduceArgs args) {
         loop.next(BM, args.reduce_shape.data(), args.reduce_strides.data());
       }
     } else {
-      for (size_t r = thread_y; r < total; r += BM) {
+      for (size_t r = start; r < end; r += BM) {
         T vals[N_READS];
         cub::LoadDirectBlocked(thread_x, in + loop.location(), vals);
         for (int i = 0; i < N_READS; i++) {
@@ -142,7 +159,7 @@ col_reduce_looped(T* in, U* out, const __grid_constant__ ColReduceArgs args) {
       }
     }
   } else {
-    for (size_t r = thread_y; r < total; r += BM) {
+    for (size_t r = start; r < end; r += BM) {
       T vals[N_READS];
       cub::LoadDirectBlocked(
           thread_x,
@@ -173,6 +190,9 @@ col_reduce_looped(T* in, U* out, const __grid_constant__ ColReduceArgs args) {
 
   // Write result.
   if (warp.thread_rank() == 0) {
+    if (BLOCKS > 1) {
+      out += tile_out * out_size * args.reduction_stride;
+    }
     cub::StoreDirectBlocked(
         warp.meta_group_rank(),
         out + tile_y * args.reduction_stride + tile_x * BN,
@@ -227,11 +247,12 @@ __global__ void col_reduce_small(
 inline auto output_grid_for_col_reduce(
     const array& out,
     const cu::ColReduceArgs& args,
-    int bn) {
+    int bn,
+    int outer = 1) {
   int gx, gy = 1;
   size_t n_inner_blocks = cuda::ceil_div(args.reduction_stride, bn);
   size_t n_outer_blocks = out.size() / args.reduction_stride;
-  size_t n_blocks = n_outer_blocks * n_inner_blocks;
+  size_t n_blocks = n_outer_blocks * n_inner_blocks * outer;
   while (n_blocks / gy > INT32_MAX) {
     gy *= 2;
   }
@@ -277,7 +298,8 @@ void col_reduce_looped(
             0,
             indata,
             gpu_ptr<U>(out),
-            static_cast<cu::ColReduceArgs>(args));
+            static_cast<cu::ColReduceArgs>(args),
+            out.size() / args.reduction_stride);
       });
     });
   });
@@ -320,6 +342,117 @@ void col_reduce_small(
   });
 }
 
+void col_reduce_two_pass(
+    cu::CommandEncoder& encoder,
+    const array& in,
+    array& out,
+    Reduce::ReduceType reduce_type,
+    const std::vector<int>& axes,
+    const ReductionPlan& plan,
+    const cu::ColReduceArgs& args) {
+  // Allocate data for the output using in's layout to access them as
+  // contiguously as possible.
+  allocate_same_layout(out, in, axes, encoder);
+
+  // Allocate an intermediate array to hold the 1st pass result
+  constexpr int outer = 32;
+
+  Shape intermediate_shape;
+  intermediate_shape.push_back(outer);
+  intermediate_shape.insert(
+      intermediate_shape.end(), out.shape().begin(), out.shape().end());
+
+  Strides intermediate_strides;
+  intermediate_strides.push_back(out.size());
+  intermediate_strides.insert(
+      intermediate_strides.end(), out.strides().begin(), out.strides().end());
+
+  array intermediate(intermediate_shape, out.dtype(), nullptr, {});
+  auto [data_size, rc, cc] =
+      check_contiguity(intermediate_shape, intermediate_strides);
+  auto fl = out.flags();
+  fl.row_contiguous = rc;
+  fl.col_contiguous = cc;
+  fl.contiguous = true;
+  intermediate.set_data(
+      cu::malloc_async(intermediate.nbytes(), encoder),
+      data_size,
+      intermediate_strides,
+      fl,
+      allocator::free);
+
+  encoder.add_temporary(intermediate);
+  encoder.set_input_array(in);
+  encoder.set_output_array(intermediate);
+  dispatch_all_types(in.dtype(), [&](auto type_tag) {
+    dispatch_reduce_ops(reduce_type, [&](auto reduce_type_tag) {
+      dispatch_reduce_ndim(args.reduce_ndim, [&](auto reduce_ndim) {
+        using OP = MLX_GET_TYPE(reduce_type_tag);
+        using T = cuda_type_t<MLX_GET_TYPE(type_tag)>;
+        using U = typename cu::ReduceResult<OP, T>::type;
+        // Cub doesn't like const pointers for vectorized loads. (sigh)
+        T* indata = const_cast<T*>(gpu_ptr<T>(in));
+
+        constexpr int N_READS = 4;
+        constexpr int BM = 32;
+        constexpr int BN = 32;
+        dim3 grid = output_grid_for_col_reduce(out, args, BN, outer);
+        int blocks = BM * BN / N_READS;
+        auto kernel = cu::
+            col_reduce_looped<T, U, OP, reduce_ndim(), BM, BN, N_READS, outer>;
+        encoder.add_kernel_node(
+            kernel,
+            grid,
+            blocks,
+            0,
+            indata,
+            gpu_ptr<U>(intermediate),
+            static_cast<cu::ColReduceArgs>(args),
+            out.size() / args.reduction_stride);
+      });
+    });
+  });
+
+  // Prepare the reduction arguments for the 2nd pass
+  cu::ColReduceArgs second_args = args;
+  second_args.reduction_size = outer;
+  second_args.reduction_stride = out.size();
+  second_args.ndim = 0;
+  second_args.reduce_shape[0] = outer;
+  second_args.reduce_strides[0] = out.size();
+  second_args.reduce_ndim = 1;
+  second_args.non_col_reductions = 1;
+
+  encoder.set_input_array(intermediate);
+  encoder.set_output_array(out);
+  dispatch_all_types(intermediate.dtype(), [&](auto type_tag) {
+    dispatch_reduce_ops(reduce_type, [&](auto reduce_type_tag) {
+      dispatch_reduce_ndim(second_args.reduce_ndim, [&](auto reduce_ndim) {
+        using OP = MLX_GET_TYPE(reduce_type_tag);
+        using T = cuda_type_t<MLX_GET_TYPE(type_tag)>;
+        using U = typename cu::ReduceResult<OP, T>::type;
+
+        constexpr int N_READS = 4;
+        constexpr int BM = 32;
+        constexpr int BN = 32;
+        dim3 grid = output_grid_for_col_reduce(out, second_args, BN);
+        int blocks = BM * BN / N_READS;
+        auto kernel =
+            cu::col_reduce_looped<T, U, OP, reduce_ndim(), BM, BN, N_READS>;
+        encoder.add_kernel_node(
+            kernel,
+            grid,
+            blocks,
+            0,
+            gpu_ptr<T>(intermediate),
+            gpu_ptr<U>(out),
+            second_args,
+            second_args.reduction_stride);
+      });
+    });
+  });
+}
+
 void col_reduce(
     cu::CommandEncoder& encoder,
     const array& in,
@@ -334,6 +467,18 @@ void col_reduce(
   //   It is a general strided reduce. Each threadblock computes the output for
   //   a subrow of the fast moving axis. For instance 32 elements.
   //
+  // - col_reduce_small
+  //
+  //  It is a column reduce for small columns. Each thread loops over the whole
+  //  column without communicating with any other thread.
+  //
+  // - col_reduce_two_pass
+  //
+  //  It is a reduce for long columns. To increase parallelism, we split the
+  //  reduction in two passes. First we do a column reduce where many
+  //  threadblocks operate on different parts of the reduced axis. Then we
+  //  perform a final column reduce.
+  //
   // Notes: As in row reduce we opt to read as much in order as possible and
   //        leave transpositions as they are (contrary to our Metal backend).
   //
@@ -349,6 +494,14 @@ void col_reduce(
     return;
   }
 
+  // Long column with smallish row
+  size_t total_sums = args.non_col_reductions * args.reduction_size;
+  size_t approx_threads = out.size();
+  if (total_sums / approx_threads > 32) {
+    col_reduce_two_pass(encoder, in, out, reduce_type, axes, plan, args);
+    return;
+  }
+
   // Fallback col reduce
   col_reduce_looped(encoder, in, out, reduce_type, axes, plan, args);
 }

mlx/backend/cuda/utils.cpp

@@ -80,7 +80,6 @@ CudaGraph::CudaGraph(cu::Device& device) {
 }
 
 void CudaGraph::end_capture(cudaStream_t stream) {
-  assert(handle_ == nullptr);
   CHECK_CUDA_ERROR(cudaStreamEndCapture(stream, &handle_));
 }
 

mlx/backend/gpu/copy.cpp

@@ -7,8 +7,6 @@
 
 namespace mlx::core {
 
-void copy_gpu(const array& in, array& out, CopyType ctype, const Stream& s);
-
 void copy_gpu(const array& in, array& out, CopyType ctype) {
   copy_gpu(in, out, ctype, out.primitive().stream());
 }

mlx/backend/metal/allocator.cpp

@@ -149,7 +149,9 @@ Buffer MetalAllocator::malloc(size_t size) {
       buf = device_->newBuffer(size, resource_options);
     }
     if (!buf) {
-      return Buffer{nullptr};
+      std::ostringstream msg;
+      msg << "[malloc] Unable to allocate " << size << " bytes.";
+      throw std::runtime_error(msg.str());
     }
     lk.lock();
     num_resources_++;
@@ -201,6 +203,32 @@ size_t MetalAllocator::size(Buffer buffer) const {
   return static_cast<MTL::Buffer*>(buffer.ptr())->length();
 }
 
+Buffer MetalAllocator::make_buffer(void* ptr, size_t size) {
+  auto buf = device_->newBuffer(ptr, size, resource_options, nullptr);
+  if (!buf) {
+    return Buffer{nullptr};
+  }
+  std::unique_lock lk(mutex_);
+  residency_set_.insert(buf);
+  active_memory_ += buf->length();
+  peak_memory_ = std::max(peak_memory_, active_memory_);
+  num_resources_++;
+  return Buffer{static_cast<void*>(buf)};
+}
+
+void MetalAllocator::release(Buffer buffer) {
+  auto buf = static_cast<MTL::Buffer*>(buffer.ptr());
+  if (buf == nullptr) {
+    return;
+  }
+  std::unique_lock lk(mutex_);
+  active_memory_ -= buf->length();
+  num_resources_--;
+  lk.unlock();
+  auto pool = metal::new_scoped_memory_pool();
+  buf->release();
+}
+
 MetalAllocator& allocator() {
   // By creating the |allocator_| on heap, the destructor of MetalAllocator
   // will not be called on exit and buffers in the cache will be leaked. This

mlx/backend/metal/allocator.h

@@ -21,6 +21,9 @@ class MetalAllocator : public allocator::Allocator {
   virtual Buffer malloc(size_t size) override;
   virtual void free(Buffer buffer) override;
   virtual size_t size(Buffer buffer) const override;
+  virtual Buffer make_buffer(void* ptr, size_t size) override;
+  virtual void release(Buffer buffer) override;
+
   size_t get_active_memory() {
     return active_memory_;
   };

mlx/backend/no_gpu/allocator.cpp

@@ -25,6 +25,7 @@ class CommonAllocator : public Allocator {
   virtual Buffer malloc(size_t size) override;
   virtual void free(Buffer buffer) override;
   virtual size_t size(Buffer buffer) const override;
+
   size_t get_active_memory() const {
     return active_memory_;
   };

mlx/distributed/CMakeLists.txt

@@ -4,6 +4,11 @@ target_sources(
           ${CMAKE_CURRENT_SOURCE_DIR}/ops.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/distributed.cpp)
 
+if(MLX_BUILD_CPU AND NOT WIN32)
+  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/utils.cpp)
+endif()
+
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/mpi)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/ring)
 add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/nccl)
+add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/jaccl)

mlx/distributed/distributed.cpp

@@ -5,6 +5,7 @@
 #include "mlx/backend/cuda/cuda.h"
 #include "mlx/distributed/distributed.h"
 #include "mlx/distributed/distributed_impl.h"
+#include "mlx/distributed/jaccl/jaccl.h"
 #include "mlx/distributed/mpi/mpi.h"
 #include "mlx/distributed/nccl/nccl.h"
 #include "mlx/distributed/ring/ring.h"
@@ -102,7 +103,27 @@ class EmptyGroup : public GroupImpl {
 } // namespace detail
 
 bool is_available() {
-  return mpi::is_available() || ring::is_available() || nccl::is_available();
+  return mpi::is_available() || ring::is_available() || nccl::is_available() ||
+      jaccl::is_available();
+}
+
+bool is_available(const std::string& bk) {
+  if (bk == "any") {
+    return is_available();
+  }
+  if (bk == "mpi") {
+    return mpi::is_available();
+  }
+  if (bk == "ring") {
+    return ring::is_available();
+  }
+  if (bk == "nccl") {
+    return nccl::is_available();
+  }
+  if (bk == "jaccl") {
+    return jaccl::is_available();
+  }
+  return false;
 }
 
 int Group::rank() const {
@@ -135,6 +156,8 @@ Group init(bool strict /* = false */, const std::string& bk /* = "any" */) {
     group = ring::init(strict);
   } else if (bk == "nccl") {
     group = nccl::init(strict);
+  } else if (bk == "jaccl") {
+    group = jaccl::init(strict);
   } else if (bk == "any") {
     if (mlx::core::cu::is_available()) {
       group = nccl::init(false);
@@ -148,13 +171,17 @@ Group init(bool strict /* = false */, const std::string& bk /* = "any" */) {
       group = mpi::init(false);
       bk_ = "mpi";
     }
+    if (group == nullptr) {
+      group = jaccl::init(false);
+      bk_ = "jaccl";
+    }
     if (group == nullptr && strict) {
       throw std::runtime_error("[distributed] Couldn't initialize any backend");
     }
   } else {
     std::ostringstream msg;
-    msg << "[distributed] The only valid values for backend are 'any', 'mpi' "
+    msg << "[distributed] The only valid values for backend are 'any', 'mpi', 'nccl', "
-        << "and 'ring' but '" << bk << "' was provided.";
+        << "'jaccl' and 'ring' but '" << bk << "' was provided.";
     throw std::invalid_argument(msg.str());
   }
 

mlx/distributed/distributed.h

@@ -16,6 +16,7 @@ class GroupImpl;
 
 /* Check if a communication backend is available */
 bool is_available();
+bool is_available(const std::string& bk);
 
 /**
  * A distributed::Group represents a group of independent mlx processes that

mlx/distributed/jaccl/CMakeLists.txt

@@ -0,0 +1,8 @@
+if(MLX_BUILD_CPU
+   AND ${CMAKE_SYSTEM_NAME} MATCHES "Darwin"
+   AND MACOS_SDK_VERSION GREATER_EQUAL 26.2)
+  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/jaccl.cpp)
+  target_link_libraries(mlx PRIVATE rdma)
+else()
+  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/no_jaccl.cpp)
+endif()

mlx/distributed/jaccl/jaccl.h

@@ -0,0 +1,12 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/distributed/distributed.h"
+
+namespace mlx::core::distributed::jaccl {
+
+using GroupImpl = mlx::core::distributed::detail::GroupImpl;
+
+bool is_available();
+std::shared_ptr<GroupImpl> init(bool strict = false);
+
+} // namespace mlx::core::distributed::jaccl

mlx/distributed/jaccl/no_jaccl.cpp

@@ -0,0 +1,20 @@
+// Copyright © 2025 Apple Inc.
+
+#include "mlx/distributed/jaccl/jaccl.h"
+
+namespace mlx::core::distributed::jaccl {
+
+using GroupImpl = mlx::core::distributed::detail::GroupImpl;
+
+bool is_available() {
+  return false;
+}
+
+std::shared_ptr<GroupImpl> init(bool strict /* = false */) {
+  if (strict) {
+    throw std::runtime_error("Cannot initialize jaccl distributed backend.");
+  }
+  return nullptr;
+}
+
+} // namespace mlx::core::distributed::jaccl

mlx/distributed/reduction_ops.h

@@ -0,0 +1,38 @@
+// Copyright © 2025 Apple Inc.
+
+namespace mlx::core::distributed::detail {
+
+template <typename T>
+struct SumOp {
+  void operator()(const T* input, T* output, size_t N) const {
+    while (N-- > 0) {
+      *output += *input;
+      input++;
+      output++;
+    }
+  }
+};
+
+template <typename T>
+struct MaxOp {
+  void operator()(const T* input, T* output, size_t N) const {
+    while (N-- > 0) {
+      *output = std::max(*output, *input);
+      input++;
+      output++;
+    }
+  }
+};
+
+template <typename T>
+struct MinOp {
+  void operator()(const T* input, T* output, size_t N) const {
+    while (N-- > 0) {
+      *output = std::min(*output, *input);
+      input++;
+      output++;
+    }
+  }
+};
+
+} // namespace mlx::core::distributed::detail

mlx/distributed/ring/ring.cpp

@@ -1,9 +1,6 @@
 // Copyright © 2024 Apple Inc.
 
-#include <arpa/inet.h>
 #include <fcntl.h>
-#include <netdb.h>
-#include <netinet/in.h>
 #include <netinet/tcp.h>
 #include <sys/socket.h>
 #include <unistd.h>
@@ -22,6 +19,8 @@
 #include "mlx/backend/cpu/encoder.h"
 #include "mlx/distributed/distributed.h"
 #include "mlx/distributed/distributed_impl.h"
+#include "mlx/distributed/reduction_ops.h"
+#include "mlx/distributed/utils.h"
 #include "mlx/threadpool.h"
 
 #ifndef SOL_TCP
@@ -94,6 +93,7 @@ constexpr const size_t ALL_SUM_SIZE = 8 * 1024 * 1024;
 constexpr const size_t ALL_SUM_BUFFERS = 2;
 constexpr const int CONN_ATTEMPTS = 5;
 constexpr const int CONN_WAIT = 1000;
+constexpr const char* RING_TAG = "[ring]";
 
 using GroupImpl = mlx::core::distributed::detail::GroupImpl;
 using json = nlohmann::json;
@@ -296,55 +296,6 @@ class CommunicationThreads {
   std::unordered_map<int, SocketThread> threads_;
 };
 
-struct address_t {
-  sockaddr_storage addr;
-  socklen_t len;
-
-  const sockaddr* get() const {
-    return (struct sockaddr*)&addr;
-  }
-};
-
-/**
- * Parse a sockaddr from an ip and port provided as strings.
- */
-address_t parse_address(const std::string& ip, const std::string& port) {
-  struct addrinfo hints, *res;
-  memset(&hints, 0, sizeof(hints));
-  hints.ai_family = AF_UNSPEC;
-  hints.ai_socktype = SOCK_STREAM;
-
-  int status = getaddrinfo(ip.c_str(), port.c_str(), &hints, &res);
-  if (status != 0) {
-    std::ostringstream msg;
-    msg << "Can't parse address " << ip << ":" << port;
-    throw std::runtime_error(msg.str());
-  }
-
-  address_t result;
-  memcpy(&result.addr, res->ai_addr, res->ai_addrlen);
-  result.len = res->ai_addrlen;
-  freeaddrinfo(res);
-
-  return result;
-}
-
-/**
- * Parse a sockaddr provided as an <ip>:<port> string.
- */
-address_t parse_address(const std::string& ip_port) {
-  auto colon = ip_port.find(":");
-  if (colon == std::string::npos) {
-    std::ostringstream msg;
-    msg << "Can't parse address " << ip_port;
-    throw std::runtime_error(msg.str());
-  }
-  std::string ip(ip_port.begin(), ip_port.begin() + colon);
-  std::string port(ip_port.begin() + colon + 1, ip_port.end());
-
-  return parse_address(ip, port);
-}
-
 /**
  * Load all addresses from the json hostfile. The hostfile is a list of
  * addresses in order of rank. For each rank there can be many addresses so
@@ -357,15 +308,15 @@ address_t parse_address(const std::string& ip_port) {
  *    ["ip3:5000", "ip3:5001"],
  *  ]
  */
-std::vector<std::vector<address_t>> load_nodes(const char* hostfile) {
+std::vector<std::vector<detail::address_t>> load_nodes(const char* hostfile) {
-  std::vector<std::vector<address_t>> nodes;
+  std::vector<std::vector<detail::address_t>> nodes;
   std::ifstream f(hostfile);
 
   json hosts = json::parse(f);
   for (auto& h : hosts) {
-    std::vector<address_t> host;
+    std::vector<detail::address_t> host;
     for (auto& ips : h) {
-      host.push_back(parse_address(ips.get<std::string>()));
+      host.push_back(std::move(detail::parse_address(ips.get<std::string>())));
     }
     nodes.push_back(std::move(host));
   }
@@ -377,73 +328,15 @@ std::vector<std::vector<address_t>> load_nodes(const char* hostfile) {
  * Create a socket and accept one connection for each of the provided
  * addresses.
  */
-std::vector<int> accept_connections(const std::vector<address_t>& addresses) {
+std::vector<int> accept_connections(
+    const std::vector<detail::address_t>& addresses) {
   std::vector<int> sockets;
   int success;
 
   for (auto& address : addresses) {
-    // Create the socket to wait for connections from the peers
+    detail::TCPSocket socket(RING_TAG);
-    int sock = socket(AF_INET, SOCK_STREAM, 0);
+    socket.listen(RING_TAG, address);
-    if (sock < 0) {
+    sockets.push_back(socket.accept(RING_TAG).detach());
-      std::ostringstream msg;
-      msg << "[ring] Couldn't create socket (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Make sure we can launch immediately after shutdown by setting the
-    // reuseaddr option so that we don't get address already in use errors
-    int enable = 1;
-    success = setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(int));
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't enable reuseaddr (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-    success = setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(int));
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't enable reuseport (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Bind the socket to the address and port
-    success = bind(sock, address.get(), address.len);
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't bind socket (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Wait for connections
-    success = listen(sock, 0);
-    if (success < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Couldn't listen (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    int peer_socket = accept(sock, nullptr, nullptr);
-    if (peer_socket < 0) {
-      shutdown(sock, 2);
-      close(sock);
-      std::ostringstream msg;
-      msg << "[ring] Accept failed (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    // Close the listening socket
-    shutdown(sock, 2);
-    close(sock);
-
-    sockets.push_back(peer_socket);
   }
 
   return sockets;
@@ -454,93 +347,42 @@ std::vector<int> accept_connections(const std::vector<address_t>& addresses) {
  * provided addresses.
  */
 std::vector<int> make_connections(
-    const std::vector<address_t>& addresses,
+    const std::vector<detail::address_t>& addresses,
     bool verbose) {
   std::vector<int> sockets;
   int success;
 
   for (auto& address : addresses) {
-    int sock;
+    sockets.push_back(detail::TCPSocket::connect(
-
+                          RING_TAG,
-    // Attempt to connect to the peer CONN_ATTEMPTS times with exponential
+                          address,
-    // backoff. TODO: Do we need that?
+                          CONN_ATTEMPTS,
-    for (int attempt = 0; attempt < CONN_ATTEMPTS; attempt++) {
+                          CONN_WAIT,
-      // Create the socket
+                          [verbose](int attempt, int wait) {
-      sock = socket(AF_INET, SOCK_STREAM, 0);
+                            log_info(
-      if (sock < 0) {
+                                verbose,
-        std::ostringstream msg;
+                                "Attempt",
-        msg << "[ring] Couldn't create socket (error: " << errno << ")";
+                                attempt,
-        throw std::runtime_error(msg.str());
+                                "waiting",
-      }
+                                wait,
-
+                                "ms (error:",
-      if (attempt > 0) {
+                                errno,
-        int wait = (1 << (attempt - 1)) * CONN_WAIT;
+                                ")");
-        log_info(
+                          })
-            verbose,
+                          .detach());
-            "Attempt",
-            attempt,
-            "wait",
-            wait,
-            "ms (error:",
-            errno,
-            ")");
-        std::this_thread::sleep_for(std::chrono::milliseconds(wait));
-      }
-
-      success = connect(sock, address.get(), address.len);
-      if (success == 0) {
-        break;
-      }
-    }
-    if (success < 0) {
-      std::ostringstream msg;
-      msg << "[ring] Couldn't connect (error: " << errno << ")";
-      throw std::runtime_error(msg.str());
-    }
-
-    sockets.push_back(sock);
   }
 
   return sockets;
 }
-template <typename T>
-struct SumOp {
-  void operator()(const T* input, T* output, size_t N) {
-    while (N-- > 0) {
-      *output += *input;
-      input++;
-      output++;
-    }
-  }
-};
-
-template <typename T>
-struct MaxOp {
-  void operator()(const T* input, T* output, size_t N) {
-    while (N-- > 0) {
-      *output = std::max(*output, *input);
-      input++;
-      output++;
-    }
-  }
-};
-
-template <typename T>
-struct MinOp {
-  void operator()(const T* input, T* output, size_t N) {
-    while (N-- > 0) {
-      *output = std::min(*output, *input);
-      input++;
-      output++;
-    }
-  }
-};
 
 } // namespace
 
 class RingGroup : public GroupImpl {
  public:
-  RingGroup(int rank, std::vector<std::vector<address_t>> nodes, bool verbose)
+  RingGroup(
+      int rank,
+      std::vector<std::vector<detail::address_t>> nodes,
+      bool verbose)
       : rank_(rank), verbose_(verbose), pool_(0) {
     if (rank_ > 0 && rank_ >= nodes.size()) {
       throw std::runtime_error(
@@ -633,17 +475,17 @@ class RingGroup : public GroupImpl {
 
   void all_sum(const array& input, array& output, Stream stream) override {
     SWITCH_TYPE(
-        output, all_reduce<T, SumOp<T>>(input, output, stream, SumOp<T>()));
+        output, all_reduce<T>(input, output, stream, detail::SumOp<T>()));
   }
 
   void all_max(const array& input, array& output, Stream stream) override {
     SWITCH_TYPE(
-        output, all_reduce<T, MaxOp<T>>(input, output, stream, MaxOp<T>()));
+        output, all_reduce<T>(input, output, stream, detail::MaxOp<T>()));
   }
 
   void all_min(const array& input, array& output, Stream stream) override {
     SWITCH_TYPE(
-        output, all_reduce<T, MinOp<T>>(input, output, stream, MinOp<T>()));
+        output, all_reduce<T>(input, output, stream, detail::MinOp<T>()));
   }
 
   std::shared_ptr<GroupImpl> split(int color, int key = -1) override {

mlx/distributed/utils.cpp

@@ -0,0 +1,204 @@
+// Copyright © 2025 Apple Inc.
+
+#include <netdb.h>
+#include <unistd.h>
+#include <cstring>
+#include <sstream>
+#include <thread>
+
+#include "mlx/distributed/utils.h"
+
+namespace mlx::core::distributed::detail {
+
+/**
+ * Parse a sockaddr from an ip and port provided as strings.
+ */
+address_t parse_address(const std::string& ip, const std::string& port) {
+  struct addrinfo hints, *res;
+  std::memset(&hints, 0, sizeof(hints));
+  hints.ai_family = AF_UNSPEC;
+  hints.ai_socktype = SOCK_STREAM;
+
+  int status = getaddrinfo(ip.c_str(), port.c_str(), &hints, &res);
+  if (status != 0) {
+    std::ostringstream msg;
+    msg << "Can't parse address " << ip << ":" << port;
+    throw std::runtime_error(msg.str());
+  }
+
+  address_t result;
+  memcpy(&result.addr, res->ai_addr, res->ai_addrlen);
+  result.len = res->ai_addrlen;
+  freeaddrinfo(res);
+
+  return result;
+}
+
+/**
+ * Parse a sockaddr provided as an <ip>:<port> string.
+ */
+address_t parse_address(const std::string& ip_port) {
+  auto colon = ip_port.find(":");
+  if (colon == std::string::npos) {
+    std::ostringstream msg;
+    msg << "Can't parse address " << ip_port;
+    throw std::runtime_error(msg.str());
+  }
+  std::string ip(ip_port.begin(), ip_port.begin() + colon);
+  std::string port(ip_port.begin() + colon + 1, ip_port.end());
+
+  return parse_address(ip, port);
+}
+
+TCPSocket::TCPSocket(const char* tag) {
+  sock_ = socket(AF_INET, SOCK_STREAM, 0);
+  if (sock_ < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't create socket (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+}
+
+TCPSocket::TCPSocket(TCPSocket&& s) {
+  sock_ = s.sock_;
+  s.sock_ = -1;
+}
+
+TCPSocket& TCPSocket::operator=(TCPSocket&& s) {
+  if (this != &s) {
+    sock_ = s.sock_;
+    s.sock_ = -1;
+  }
+  return *this;
+}
+
+TCPSocket::TCPSocket(int s) : sock_(s) {}
+
+TCPSocket::~TCPSocket() {
+  if (sock_ > 0) {
+    shutdown(sock_, 2);
+    close(sock_);
+  }
+}
+
+int TCPSocket::detach() {
+  int s = sock_;
+  sock_ = -1;
+  return s;
+}
+
+void TCPSocket::listen(const char* tag, const address_t& addr) {
+  int success;
+
+  // Make sure we can launch immediately after shutdown by setting the
+  // reuseaddr option so that we don't get address already in use errors
+  int enable = 1;
+  success = setsockopt(sock_, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(int));
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't enable reuseaddr (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+  success = setsockopt(sock_, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(int));
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't enable reuseport (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  // Bind the socket to the address and port
+  success = bind(sock_, addr.get(), addr.len);
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't bind socket (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  // Prepare waiting for connections
+  success = ::listen(sock_, 0);
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't listen (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+}
+
+TCPSocket TCPSocket::accept(const char* tag) {
+  int peer = ::accept(sock_, nullptr, nullptr);
+  if (peer < 0) {
+    std::ostringstream msg;
+    msg << tag << " Accept failed (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  return TCPSocket(peer);
+}
+
+void TCPSocket::send(const char* tag, const void* data, size_t len) {
+  while (len > 0) {
+    auto n = ::send(sock_, data, len, 0);
+    if (n <= 0) {
+      std::ostringstream msg;
+      msg << tag << " Send failed with errno=" << errno;
+      throw std::runtime_error(msg.str());
+    }
+    len -= n;
+    data = static_cast<const char*>(data) + n;
+  }
+}
+
+void TCPSocket::recv(const char* tag, void* data, size_t len) {
+  while (len > 0) {
+    auto n = ::recv(sock_, data, len, 0);
+    if (n <= 0) {
+      std::ostringstream msg;
+      msg << tag << " Recv failed with errno=" << errno;
+      throw std::runtime_error(msg.str());
+    }
+    len -= n;
+    data = static_cast<char*>(data) + n;
+  }
+}
+
+TCPSocket TCPSocket::connect(
+    const char* tag,
+    const address_t& addr,
+    int num_retries,
+    int wait,
+    std::function<void(int, int)> cb) {
+  int sock, success;
+
+  // Attempt to connect `num_retries` times with exponential backoff.
+  for (int attempt = 0; attempt < num_retries; attempt++) {
+    // Create the socket
+    sock = socket(AF_INET, SOCK_STREAM, 0);
+    if (sock < 0) {
+      std::ostringstream msg;
+      msg << tag << " Couldn't create socket to connect (error: " << errno
+          << ")";
+      throw std::runtime_error(msg.str());
+    }
+
+    success = ::connect(sock, addr.get(), addr.len);
+    if (success == 0) {
+      break;
+    }
+
+    cb(attempt, wait);
+    if (wait > 0) {
+      std::this_thread::sleep_for(std::chrono::milliseconds(wait));
+    }
+
+    wait <<= 1;
+  }
+
+  if (success < 0) {
+    std::ostringstream msg;
+    msg << tag << " Couldn't connect (error: " << errno << ")";
+    throw std::runtime_error(msg.str());
+  }
+
+  return TCPSocket(sock);
+}
+
+} // namespace mlx::core::distributed::detail

mlx/distributed/utils.h

@@ -0,0 +1,67 @@
+// Copyright © 2025 Apple Inc.
+
+#pragma once
+
+#include <sys/socket.h>
+#include <functional>
+#include <string>
+
+namespace mlx::core::distributed::detail {
+
+struct address_t {
+  sockaddr_storage addr;
+  socklen_t len;
+
+  const sockaddr* get() const {
+    return (struct sockaddr*)&addr;
+  }
+};
+
+/**
+ * Parse a sockaddr from an ip and port provided as strings.
+ */
+address_t parse_address(const std::string& ip, const std::string& port);
+
+/**
+ * Parse a sockaddr provided as an <ip>:<port> string.
+ */
+address_t parse_address(const std::string& ip_port);
+
+/**
+ * Small wrapper over a TCP socket to simplify initiating connections.
+ */
+class TCPSocket {
+ public:
+  TCPSocket(const char* tag);
+  TCPSocket(const TCPSocket&) = delete;
+  TCPSocket& operator=(const TCPSocket&) = delete;
+  TCPSocket(TCPSocket&& s);
+  TCPSocket& operator=(TCPSocket&&);
+  ~TCPSocket();
+
+  void listen(const char* tag, const address_t& addr);
+  TCPSocket accept(const char* tag);
+
+  void send(const char* tag, const void* data, size_t len);
+  void recv(const char* tag, void* data, size_t len);
+
+  int detach();
+
+  operator int() const {
+    return sock_;
+  }
+
+  static TCPSocket connect(
+      const char* tag,
+      const address_t& addr,
+      int num_retries = 1,
+      int wait = 0,
+      std::function<void(int, int)> cb = nullptr);
+
+ private:
+  TCPSocket(int sock);
+
+  int sock_;
+};
+
+} // namespace mlx::core::distributed::detail

python/mlx/_distributed_utils/common.py

@@ -0,0 +1,95 @@
+# Copyright © 2025 Apple Inc.
+
+import argparse
+import ipaddress
+import json
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Optional
+
+
+@dataclass
+class Host:
+    rank: int
+    ssh_hostname: str
+    ips: list[str]
+    rdma: list[Optional[str]]
+
+
+class OptionalBoolAction(argparse.Action):
+    def __call__(self, parser, namespace, values, option_string=None):
+        if option_string.startswith("--no-"):
+            setattr(namespace, self.dest, False)
+        else:
+            setattr(namespace, self.dest, True)
+
+
+def positive_number(x):
+    x = int(x)
+    if x <= 0:
+        raise ValueError("Number should be positive")
+    return x
+
+
+def log(verbose, *args, **kwargs):
+    if not verbose:
+        return
+    kwargs["file"] = sys.stderr
+    print("\033[32m[INFO]", *args, "\033[0m", **kwargs)
+
+
+def log_warning(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print("\033[33m[WARN]", *args, "\033[0m", **kwargs)
+
+
+def log_error(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print("\033[31m[ERROR]", *args, "\033[0m", **kwargs)
+
+
+def parse_hostlist(parser, hostlist, repeats):
+    hosts = []
+    for i, h in enumerate(hostlist.split(",")):
+        if h == "":
+            raise ValueError("Hostname cannot be empty")
+        try:
+            ipaddress.ip_address(h)
+            ips = [h]
+        except ValueError:
+            ips = []
+        for i in range(repeats):
+            hosts.append(Host(i, h, ips, []))
+    return hosts
+
+
+def parse_hostfile(parser, hostfile):
+    """Parse the json hostfile that contains both the hostnames to ssh into and
+    the ips to communicate over when using the ring backend.
+
+    Example:
+
+        [
+            {"ssh": "hostname1", "ips": ["123.123.123.1"], "rdma": [null, "rdma_en2", "rdma_en3"]},
+            {"ssh": "hostname2", "ips": ["123.123.123.2"], "rdma": ["rdma_en2", null, "rdma_en3"]},
+            ...
+            {"ssh": "hostnameN", "ips": ["123.123.123.N"], "rdma": ["rdma_en2", "rdma_en3", null]},
+        ]
+
+    Args:
+        hostfile (str): The path to the json file containing the host
+            information
+    """
+    hostfile = Path(hostfile)
+    if not hostfile.exists():
+        parser.error(f"Hostfile {str(hostfile)} doesn't exist")
+
+    try:
+        hosts = []
+        with open(hostfile) as f:
+            for i, h in enumerate(json.load(f)):
+                hosts.append(Host(i, h["ssh"], h.get("ips", []), h.get("rdma", [])))
+        return hosts
+    except Exception as e:
+        parser.error(f"Failed to parse hostfile {str(hostfile)} ({str(e)})")

python/mlx/_distributed_utils/config.py

@@ -0,0 +1,570 @@
+# Copyright © 2025 Apple Inc.
+
+import argparse
+import json
+import shlex
+import sys
+import threading
+from collections import defaultdict
+from dataclasses import dataclass
+from subprocess import DEVNULL, run
+from typing import Optional
+
+import mlx.core as mx
+
+from .common import (
+    Host,
+    OptionalBoolAction,
+    log,
+    log_error,
+    parse_hostfile,
+    parse_hostlist,
+)
+
+
+@dataclass
+class SSHInfo:
+    can_ssh: bool
+    has_sudo: bool
+
+    def __bool__(self):
+        return self.can_ssh
+
+
+@dataclass
+class ThunderboltPort:
+    iface: str
+    uuid: str
+    connected_to: Optional[str]
+
+
+@dataclass
+class ThunderboltHost:
+    name: str
+    ports: list[ThunderboltPort]
+
+
+def add_ethernet_ips(hosts, verbose=False):
+    # Get the ips for each host
+    for h in hosts:
+        log(verbose, "Getting the ip from", h.ssh_hostname)
+        h.ips.append(
+            run(
+                ["ssh", h.ssh_hostname, "ipconfig", "getifaddr", "en0"],
+                capture_output=True,
+                text=True,
+            ).stdout.strip()
+        )
+
+
+def check_rdma(hosts, verbose=False):
+    # Check whether the hosts are capable of RDMA over thunderbolt
+    warn = False
+    for h in hosts:
+        log(verbose, "Checking that", h.ssh_hostname, "supports RDMA")
+        rdma_devs = (
+            run(["ssh", h.ssh_hostname, "ibv_devices"], capture_output=True, text=True)
+            .stdout.strip()
+            .split()
+        )
+        rdma_devs = [d for d in rdma_devs if d.startswith("rdma_")]
+        if not rdma_devs:
+            log_warning(h.ssh_hostname, "does not seem to have RDMA enabled")
+            warn = True
+
+    if warn:
+        log_warning()
+        log_warning(
+            "Some of the hosts don't have RDMA enabled or they don't support RDMA."
+        )
+        log_warning()
+        log_warning(
+            "See https://ml-explore.github.io/mlx/build/html/usage/distributed.html"
+        )
+        log_warning("for instructions on how to enable RDMA.")
+
+
+def can_auto_setup(hosts, sshinfo, auto_setup=False):
+    has_sudo = all(info.has_sudo for info in sshinfo)
+    if not has_sudo and auto_setup:
+        log_warning(
+            "Automatic setup requested but the following hosts do not have passwordless sudo"
+        )
+        for h, i in zip(hosts, sshinfo):
+            if not i.has_sudo:
+                log_warning(" - ", h.ssh_hostname)
+    return has_sudo
+
+
+class IPConfigurator:
+    def __init__(self, hosts, tb_hosts, uuid_reverse_index):
+        assigned = set()
+        ips = defaultdict(list)
+        ip0 = 0
+        ip1 = 0
+        for src_node, h in enumerate(tb_hosts):
+            for src_port, p in enumerate(h.ports):
+                if not p.connected_to:
+                    continue
+                if p.connected_to not in uuid_reverse_index:
+                    continue
+                if (src_node, src_port) in assigned:
+                    continue
+
+                dst_node, dst_port = uuid_reverse_index[p.connected_to]
+
+                ip_src = f"192.168.{ip0}.{ip1 + 1}"
+                ip_dst = f"192.168.{ip0}.{ip1 + 2}"
+                iface_src = p.iface
+                iface_dst = tb_hosts[dst_node].ports[dst_port].iface
+
+                ips[src_node, dst_node].append((iface_src, ip_src))
+                ips[dst_node, src_node].append((iface_dst, ip_dst))
+
+                assigned.add((src_node, src_port))
+                assigned.add((dst_node, dst_port))
+
+                ip1 += 4
+                if ip1 > 255:
+                    ip0 += 1
+                    ip1 = 0
+                if ip0 > 255:
+                    raise ValueError("Ran out of available local IPs")
+
+        self.ips = ips
+        self.hosts = hosts
+        self.tb_hosts = tb_hosts
+
+    def setup(self, verbose=False, auto_setup=False):
+        netmask = "255.255.255.252"
+        for i, (h, th) in enumerate(zip(self.hosts, self.tb_hosts)):
+            command = ""
+            command += "sudo ifconfig bridge0 down\n"
+            for j in range(len(self.hosts)):
+                if i == j or (i, j) not in self.ips:
+                    continue
+                for (iface, ip), (_, peer) in zip(self.ips[i, j], self.ips[j, i]):
+                    command += f"sudo ifconfig {iface} inet {ip} netmask {netmask}\n"
+                    command += f"sudo route change {peer} -interface {iface}\n"
+            if auto_setup:
+                print(f"Running auto setup for {h.ssh_hostname}")
+                command = command.strip().replace("\n", " ; ")
+                command = ["ssh", h.ssh_hostname, command]
+                log(verbose, shlex.join(command))
+                run(command)
+            else:
+                msg = f"Setup for {h.ssh_hostname}"
+                print(msg)
+                print("=" * len(msg))
+                print(command)
+                input("Enter to continue")
+            print()
+
+
+def parse_hardware_ports(ports_string):
+    ports = {}
+    port_name = None
+    for l in ports_string.decode("utf-8").split("\n"):
+        if l.startswith("Hardware Port:"):
+            port_name = l.strip()[15:]
+        elif l.startswith("Device:"):
+            ports[port_name] = l.strip()[8:]
+            port_name = None
+    return ports
+
+
+def extract_connectivity(hosts, verbose):
+    # Extract the current connectivity from the remote hosts
+    thunderbolt_connections = []
+    for h in hosts:
+        log(verbose, "Getting connectivity from", h.ssh_hostname)
+        thunderbolt_connections.append(
+            json.loads(
+                run(
+                    [
+                        "ssh",
+                        h.ssh_hostname,
+                        "system_profiler",
+                        "SPThunderboltDataType",
+                        "-json",
+                    ],
+                    capture_output=True,
+                ).stdout
+            )
+        )
+    interface_maps = []
+    for h in hosts:
+        log(verbose, "Getting interface names from", h.ssh_hostname)
+        interface_maps.append(
+            parse_hardware_ports(
+                run(
+                    [
+                        "ssh",
+                        h.ssh_hostname,
+                        "networksetup",
+                        "-listallhardwareports",
+                    ],
+                    capture_output=True,
+                ).stdout
+            )
+        )
+
+    # Parse the connectivity into some simple dataclasses
+    tb_hosts = []
+    for c, iface_map in zip(thunderbolt_connections, interface_maps):
+        name = ""
+        ports = []
+        for t in c["SPThunderboltDataType"]:
+            uuid = t.get("domain_uuid_key")
+            if uuid is None:
+                continue
+            name = t["device_name_key"]
+            tag = t["receptacle_1_tag"]["receptacle_id_key"]
+            items = t.get("_items", [])
+            connected_items = [item for item in items if "domain_uuid_key" in item]
+            connected_to = (
+                connected_items[0]["domain_uuid_key"] if connected_items else None
+            )
+            iface = iface_map[f"Thunderbolt {tag}"]
+            ports.append(ThunderboltPort(iface, uuid, connected_to))
+        tb_hosts.append(ThunderboltHost(name, sorted(ports, key=lambda x: x.iface)))
+
+    # Create a reverse index to be able to map uuids to (host, port) quickly
+    uuid_reverse_index = {}
+    for i, h in enumerate(tb_hosts):
+        for j, p in enumerate(h.ports):
+            uuid_reverse_index[p.uuid] = (i, j)
+
+    return tb_hosts, uuid_reverse_index
+
+
+def make_connectivity_matrix(tb_hosts, uuid_reverse_index):
+    connectivity = []
+    for i, h in enumerate(tb_hosts):
+        c = [0] * len(tb_hosts)
+        for p in h.ports:
+            if p.connected_to in uuid_reverse_index:
+                j, _ = uuid_reverse_index[p.connected_to]
+                c[j] += 1
+        connectivity.append(c)
+    return connectivity
+
+
+def tb_connectivity_to_dot(hosts, tb_hosts, uuid_reverse_index):
+    # Make ids per node
+    names = []
+    for i in range(len(tb_hosts)):
+        n = ""
+        j = i
+        while True:
+            n += chr(97 + j % 26)
+            j //= 26
+            if j == 0:
+                break
+        names.append(n)
+
+    print("graph G {")
+    print("  node [shape=rectangle];")
+    for i, h in enumerate(hosts):
+        print(f'  {names[i]} [label="{h.ssh_hostname}"];')
+    for i, h in enumerate(tb_hosts):
+        for p in h.ports:
+            if not p.connected_to:
+                continue
+            dst = uuid_reverse_index[p.connected_to]
+            if dst[0] < i:
+                continue
+            print(f"  {names[i]} -- {names[dst[0]]}", end="")
+            print(f' [label="{p.iface}/{tb_hosts[dst[0]].ports[dst[1]].iface}"]')
+    print("}")
+
+
+def extract_rings(connectivity):
+    rings = []
+    existing_rings = set()
+    num_nodes = len(connectivity)
+
+    def dfs(start_node, node, path, visited):
+        path.append(node)
+        visited.add(node)
+        for j in range(num_nodes):
+            if connectivity[node][j] <= 0:
+                continue
+            if j == start_node:
+                yield path[:]
+            if j not in visited:
+                yield from dfs(start_node, j, path, visited)
+        path.pop()
+        visited.remove(node)
+
+    for start in range(num_nodes):
+        for r in dfs(start, start, [], set()):
+            cnt = min(connectivity[r[i]][r[(i + 1) % len(r)]] for i in range(len(r)))
+            rkey = tuple(sorted(r))
+            if rkey not in existing_rings:
+                rings.append((r, cnt))
+                existing_rings.add(rkey)
+
+    return sorted(rings, key=lambda x: -len(x[0]))
+
+
+def check_valid_mesh(hosts, connectivity, strict=True):
+    num_nodes = len(connectivity)
+    for i in range(num_nodes):
+        for j in range(num_nodes):
+            if i == j:
+                continue
+            if connectivity[i][j] <= 0:
+                if strict:
+                    log_error(
+                        f"Incomplete mesh, {hosts[i].ssh_hostname} is not connected to {hosts[j].ssh_hostname}"
+                    )
+                    log_error()
+                    log_error("Try passing --dot to visualize the connectivity")
+                    sys.exit(1)
+                else:
+                    return False
+    return True
+
+
+def check_ssh_connections(hosts):
+    results = [None] * len(hosts)
+
+    def _check(hostname, i):
+        info = SSHInfo(False, False)
+        results[i] = info
+
+        # Check for ssh
+        result = run(
+            [
+                "ssh",
+                "-o",
+                "BatchMode=yes",
+                "-o",
+                "ConnectTimeout=5",
+                hostname,
+                "echo",
+                "success",
+            ],
+            stdout=DEVNULL,
+            stderr=DEVNULL,
+        )
+        info.can_ssh = result.returncode == 0
+        if not info.can_ssh:
+            return
+
+        # Check for sudo
+        result = run(
+            [
+                "ssh",
+                "-o",
+                "BatchMode=yes",
+                "-o",
+                "ConnectTimeout=5",
+                hostname,
+                "sudo",
+                "ls",
+            ],
+            stdout=DEVNULL,
+            stderr=DEVNULL,
+        )
+        info.has_sudo = result.returncode == 0
+
+    threads = [
+        threading.Thread(target=_check, args=(h.ssh_hostname, i))
+        for i, h in enumerate(hosts)
+    ]
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+
+    if not all(results):
+        log_error("Could not ssh to the following hosts:")
+        for i, h in enumerate(hosts):
+            if not results[i]:
+                log_error("  - ", h.ssh_hostname)
+        log_error()
+        log_error("Maybe they are not set-up for password-less ssh?")
+        sys.exit(1)
+
+    return results
+
+
+def prepare_ethernet_hostfile(args, hosts):
+    log(args.verbose, f"Preparing an ethernet hostfile")
+    add_ethernet_ips(hosts, args.verbose)
+
+    hostfile = []
+    for h in hosts:
+        hostfile.append(dict(ssh=h.ssh_hostname, ips=h.ips))
+
+    if args.output_hostfile:
+        with open(args.output_hostfile, "w") as f:
+            json.dump(hostfile, f, indent=4)
+    else:
+        print("Hostfile")
+        print("========")
+        print(json.dumps(hostfile, indent=4))
+
+
+def configure_ring(args, hosts, ips, ring, sshinfo):
+    log(args.verbose, "Prepare a ring hostfile")
+    ring, count = ring
+    hostfile = []
+    for i, node in enumerate(ring):
+        h = hosts[node]
+        peer = ring[i - 1]
+        hostfile.append(
+            {
+                "ssh": h.ssh_hostname,
+                "ips": [ips.ips[node, peer][c][1] for c in range(count)],
+                "rdma": [],
+            }
+        )
+
+    has_sudo = can_auto_setup(hosts, sshinfo, args.auto_setup)
+    ips.setup(verbose=args.verbose, auto_setup=args.auto_setup and has_sudo)
+
+    if args.output_hostfile:
+        with open(args.output_hostfile, "w") as f:
+            json.dump(hostfile, f, indent=4)
+    else:
+        print("Hostfile")
+        print("========")
+        print(json.dumps(hostfile, indent=4))
+
+
+def configure_jaccl(args, hosts, ips, sshinfo):
+    log(args.verbose, "Prepare a jaccl hostfile")
+    check_rdma(hosts, args.verbose)
+    add_ethernet_ips(hosts, args.verbose)
+
+    hostfile = []
+    for i, h in enumerate(hosts):
+        rdma = []
+        for j in range(len(hosts)):
+            if i == j:
+                rdma.append(None)
+            else:
+                rdma.append(f"rdma_{ips.ips[i, j][0][0]}")
+        hostfile.append({"ssh": h.ssh_hostname, "ips": h.ips, "rdma": rdma})
+
+    has_sudo = can_auto_setup(hosts, sshinfo, args.auto_setup)
+    ips.setup(verbose=args.verbose, auto_setup=args.auto_setup and has_sudo)
+
+    if args.output_hostfile:
+        with open(args.output_hostfile, "w") as f:
+            json.dump(hostfile, f, indent=4)
+    else:
+        print("Hostfile")
+        print("========")
+        print(json.dumps(hostfile, indent=4))
+
+
+def prepare_tb_hostfile(args, hosts, sshinfo):
+    log(args.verbose, f"Preparing for communication over thunderbolt")
+    tb_hosts, uuid_reverse_index = extract_connectivity(hosts, args.verbose)
+
+    if args.dot:
+        tb_connectivity_to_dot(hosts, tb_hosts, uuid_reverse_index)
+        return
+
+    ips = IPConfigurator(hosts, tb_hosts, uuid_reverse_index)
+    connectivity = make_connectivity_matrix(tb_hosts, uuid_reverse_index)
+
+    if args.backend is None:
+        rings = extract_rings(connectivity)
+        has_mesh = check_valid_mesh(hosts, connectivity, False)
+        has_ring = len(rings) > 0 and len(rings[0][0]) == len(hosts)
+
+        if not has_ring and not has_mesh:
+            log_error("Neither thunderbolt mesh nor ring found.")
+            log_error("Perhaps run with --dot to generate a plot of the connectivity.")
+            sys.exit(1)
+
+        elif has_ring:
+            configure_ring(args, hosts, ips, rings[0], sshinfo)
+
+        else:
+            configure_jaccl(args, hosts, ips, sshinfo)
+
+    elif args.backend == "ring":
+        rings = extract_rings(connectivity)
+        has_ring = len(rings) > 0 and len(rings[0][0]) == len(hosts)
+        if not has_ring:
+            log_error("Could not find a full ring.")
+            log_error()
+            log_error("Try passing --dot to visualize the connectivity")
+            if len(rings) > 0:
+                log_error("Rings found:")
+                for r in rings:
+                    log_error(f" - {','.join(hosts[i].ssh_hostname for i in r)}")
+            sys.exit(1)
+        configure_ring(args, hosts, ips, rings[0], sshinfo)
+
+    elif args.backend == "jaccl":
+        check_valid_mesh(hosts, connectivity)
+        configure_jaccl(args, hosts, ips, sshinfo)
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Configure remote machines for use with MLX distributed"
+    )
+    parser.add_argument(
+        "--verbose", action="store_true", help="Print debug messages in stdout"
+    )
+    parser.add_argument(
+        "--hosts", default="127.0.0.1", help="A comma separated list of hosts"
+    )
+    parser.add_argument("--hostfile", help="The file containing the hosts")
+    parser.add_argument(
+        "--over",
+        choices=["thunderbolt", "ethernet"],
+        default="thunderbolt",
+        help="What type of connectivity to configure",
+        required=True,
+    )
+    parser.add_argument(
+        "--output-hostfile", help="If provided, save the hostfile to this path"
+    )
+    parser.add_argument(
+        "--auto-setup",
+        "--no-auto-setup",
+        action=OptionalBoolAction,
+        nargs=0,
+        dest="auto_setup",
+        default=None,
+    )
+    parser.add_argument(
+        "--dot", action="store_true", help="Output the topology in DOT format and exit"
+    )
+    parser.add_argument(
+        "--backend",
+        choices=["ring", "jaccl"],
+        default=None,
+        help="Which distributed backend to configure",
+    )
+    args = parser.parse_args()
+
+    if args.hostfile is not None:
+        hosts = parse_hostfile(parser, args.hostfile)
+    else:
+        hosts = parse_hostlist(parser, args.hosts, 1)
+
+    # Check that we can ssh
+    log(
+        args.verbose,
+        f"Checking for ssh access for {', '.join(h.ssh_hostname for h in hosts)}",
+    )
+    sshinfo = check_ssh_connections(hosts)
+
+    # Prepare a hostfile for communication over ethernet using the ips of the
+    # provided hostnames
+    if args.over == "ethernet":
+        prepare_ethernet_hostfile(args, hosts)
+
+    # Configure the macs for communication over thunderbolt, both via RDMA and IP
+    else:
+        prepare_tb_hostfile(args, hosts, sshinfo)

python/mlx/_distributed_utils/launch.py

@@ -0,0 +1,557 @@
+# Copyright © 2025 Apple Inc.
+
+import argparse
+import base64
+import json
+import os
+import shlex
+import shutil
+import sys
+import tempfile
+import threading
+from collections import Counter
+from itertools import chain
+from pathlib import Path
+from queue import Empty as QueueEmpty
+from queue import Queue
+from select import select
+from subprocess import PIPE, Popen, run
+
+import mlx.core as mx
+
+from .common import log, log_warning, parse_hostfile, parse_hostlist, positive_number
+
+
+class CommandProcess:
+    @property
+    def process(self):
+        """Return the Popen object that refers to the current command."""
+        raise NotImplementedError()
+
+    @property
+    def exit_status(self):
+        """Return a tuple (returncode, killed) for the command. It should be
+        (None, None) while the command is running normally."""
+        raise NotImplementedError()
+
+    def preprocess_output(self, data: str, is_stdout=False):
+        """Preprocess the output of the command so that extra data can be
+        capture or the format changed on the fly."""
+        raise NotImplementedError()
+
+    def terminate(self):
+        """Terminate or return the exit code."""
+        raise NotImplementedError()
+
+
+class RemoteProcess(CommandProcess):
+    def __init__(self, rank, host, python, cwd, files, env, command):
+        is_local = host == "127.0.0.1"
+        cmd = RemoteProcess.make_launch_script(rank, cwd, files, env, command)
+        if not is_local:
+            cmd = f"ssh -tt -o LogLevel=QUIET {host} {shlex.quote(cmd)}"
+
+        self._host = host
+        self._pidfile = None
+        self._is_local = is_local
+        self._process = Popen(
+            cmd,
+            shell=True,
+            executable="/bin/bash",
+            stdin=PIPE,
+            stdout=PIPE,
+            stderr=PIPE,
+        )
+
+        self._killed = False
+
+    @property
+    def process(self):
+        return self._process
+
+    @property
+    def exit_status(self):
+        return self._process.poll(), self._killed
+
+    def preprocess_output(self, data, is_stdout=False):
+        if self._pidfile is None:
+            pidfile, *rest = data.split("\n", maxsplit=1)
+            self._pidfile = pidfile
+            return rest[0] if rest else ""
+
+        return data
+
+    def terminate(self):
+        if self._killed:
+            return
+
+        self._process.terminate()
+        self._process.wait()
+
+        # Kill the remote program if possible
+        cmd = RemoteProcess.make_kill_script(self._pidfile)
+        if not self._is_local:
+            cmd = f"ssh {self._host} {shlex.quote(cmd)}"
+        c = run(
+            cmd,
+            check=True,
+            shell=True,
+            executable="/bin/bash",
+            capture_output=True,
+            text=True,
+        )
+
+        self._killed = c.stdout.strip() == "1"
+
+    @staticmethod
+    def make_launch_script(rank, cwd, files, env, command):
+        script = ""
+
+        # Disable echo
+        script = "stty -echo; "
+
+        # Write the PID to a file so we can kill the process if needed
+        script += "pidfile=$(mktemp); "
+        script += "echo $$ > $pidfile; "
+        script += 'printf "%s\\n" $pidfile; '
+
+        # Change the working directory if one was requested. Otherwise attempt to
+        # change to the current one but don't fail if it wasn't possible.
+        d = cwd or os.getcwd()
+        script += f"if [[ -d {repr(d)} ]]; then "
+        script += f"  cd {repr(d)}; "
+        if cwd is not None:
+            script += "else "
+            script += f" echo 'Failed to change directory to' {repr(d)} >2; "
+        script += "fi; "
+
+        # Add the environment variables that were requested
+        for e in env:
+            key, *value = e.split("=", maxsplit=1)
+            value = shlex.quote(value[0]) if len(value) > 0 else ""
+            if not all(c.isalnum() or c == "_" for c in key):
+                log_warning(
+                    f"'{e}' is an invalid environment variable so it is ignored"
+                )
+                continue
+            script += f"export {key}={value}; "
+
+        # Make the temporary files
+        for env_name, content in files.items():
+            script += "fname=$(mktemp); "
+            script += f"echo {shlex.quote(content)} >$fname; "
+            script += f"export {env_name}=$fname; "
+
+        # Finally add the rank
+        script += f"export MLX_RANK={rank}; "
+
+        # Replace the process with the script
+        script += f"cmd=({' '.join(map(shlex.quote, command))}); "
+        script += 'exec "${cmd[@]}"'
+
+        return script
+
+    @staticmethod
+    def make_kill_script(pidfile):
+        script = ""
+        script += f"pid=$(cat {pidfile}); "
+        script += "if ps -p $pid >/dev/null; then "
+        script += "    kill $pid; "
+        script += "    echo 1; "
+        script += "else "
+        script += "    echo 0; "
+        script += "fi; "
+        script += f"rm {pidfile}"
+
+        return script
+
+
+def _launch_with_io(command_class, arguments, verbose):
+    stop = False
+    exit_codes = [(None, None)] * len(arguments)
+
+    def _thread_fn(rank, *args, **kwargs):
+        stdin_queue = kwargs.pop("stdin_queue")
+        stdout_queue = kwargs.pop("stdout_queue")
+        stderr_queue = kwargs.pop("stderr_queue")
+
+        command = command_class(rank, *args, **kwargs)
+        p = command.process
+        os.set_blocking(p.stdout.fileno(), False)
+        os.set_blocking(p.stderr.fileno(), False)
+        os.set_blocking(p.stdin.fileno(), False)
+
+        to_read = [p.stdout.fileno(), p.stderr.fileno()]
+        to_write = [p.stdin.fileno()]
+
+        stdin_buffer = b""
+        while p.poll() is None:
+            try:
+                stdin_buffer += stdin_queue.get_nowait()
+            except QueueEmpty:
+                pass
+            rlist, wlist, _ = select(to_read, to_write, [], 1.0)
+            for fd in rlist:
+                is_stdout = fd == p.stdout.fileno()
+                msg = os.read(fd, 8192).decode(errors="ignore")
+                msg = command.preprocess_output(msg, is_stdout)
+                if is_stdout:
+                    stdout_queue.put(msg.encode())
+                else:
+                    stderr_queue.put(msg.encode())
+            for fd in wlist:
+                if len(stdin_buffer) > 0:
+                    n = os.write(fd, stdin_buffer)
+                    stdin_buffer = stdin_buffer[n:]
+            if stop:
+                command.terminate()
+                break
+        exit_codes[rank] = command.exit_status
+
+        if exit_codes[rank][1]:
+            log_warning(f"Node with rank {rank} was killed")
+        elif exit_codes[rank][0] != 0:
+            log_warning(f"Node with rank {rank} exited with code {exit_codes[rank][0]}")
+        else:
+            log(verbose, f"Node with rank {rank} completed")
+
+    stdin_queues = []
+    stdout_queues = []
+    stderr_queues = []
+    threads = []
+    for i, (args, kwargs) in enumerate(arguments):
+        stdin_queues.append(Queue())
+        stdout_queues.append(Queue())
+        stderr_queues.append(Queue())
+        t = threading.Thread(
+            target=_thread_fn,
+            args=args,
+            kwargs=kwargs
+            | {
+                "stdin_queue": stdin_queues[-1],
+                "stdout_queue": stdout_queues[-1],
+                "stderr_queue": stderr_queues[-1],
+            },
+        )
+        t.start()
+        threads.append(t)
+
+    os.set_blocking(sys.stdin.fileno(), False)
+    os.set_blocking(sys.stdout.fileno(), True)
+    os.set_blocking(sys.stderr.fileno(), True)
+    while not stop or any(not q.empty() for q in chain(stdout_queues, stderr_queues)):
+        # Broadcast user input to the jobs
+        rlist, _, _ = select([sys.stdin.fileno()], [], [], 0.1)
+        for fd in rlist:
+            stdin_buffer = os.read(fd, 8192)
+            for q in stdin_queues:
+                q.put(stdin_buffer)
+
+        # Gather job output
+        for q in stdout_queues:
+            try:
+                while not q.empty():
+                    sys.stdout.buffer.write(q.get_nowait())
+            except QueueEmpty:
+                pass
+        for q in stderr_queues:
+            try:
+                while not q.empty():
+                    sys.stderr.buffer.write(q.get_nowait())
+            except QueueEmpty:
+                pass
+        sys.stdout.buffer.flush()
+        sys.stderr.buffer.flush()
+
+        # Check if all are running and terminate otherwise
+        if any(t.is_alive() for t in threads):
+            for i, t in enumerate(threads):
+                if not t.is_alive():
+                    if exit_codes[i][0] != 0:
+                        stop = True
+                        break
+        else:
+            break
+
+    # Wait for the jobs to finish
+    for t in threads:
+        t.join()
+
+    # Process any remaining outputs
+    for q in stdout_queues:
+        while not q.empty():
+            sys.stdout.buffer.write(q.get())
+    for q in stderr_queues:
+        while not q.empty():
+            sys.stderr.buffer.write(q.get())
+    sys.stdout.buffer.flush()
+    sys.stderr.buffer.flush()
+
+
+def launch_ring(parser, hosts, args, command):
+    if any(len(h.ips) == 0 for h in hosts):
+        parser.error(
+            "The ring backend requires IPs to be provided instead of hostnames"
+        )
+
+    port = args.starting_port
+    ring_hosts = []
+    for h in hosts:
+        node = []
+        for ip in h.ips:
+            for i in range(args.connections_per_ip):
+                node.append(f"{ip}:{port}")
+                port += 1
+        ring_hosts.append(node)
+    hostfile = json.dumps(ring_hosts) if len(ring_hosts) > 1 else ""
+
+    files = {"MLX_HOSTFILE": hostfile}
+    env = args.env
+    if args.verbose:
+        env.append("MLX_RING_VERBOSE=1")
+    cwd = args.cwd
+
+    log(args.verbose, "Running", shlex.join(command))
+
+    _launch_with_io(
+        RemoteProcess,
+        [
+            ((rank, h.ssh_hostname, args.python, cwd, files, env, command), {})
+            for rank, h in enumerate(hosts)
+        ],
+        args.verbose,
+    )
+
+
+def launch_nccl(parser, hosts, args, command):
+    if not hosts[0].ips:
+        raise ValueError("Rank 0 should have an IP reachable from all other ranks")
+
+    master_host = hosts[0].ips[0]
+    master_port = args.nccl_port
+    world_size = len(hosts)
+
+    env = args.env
+    cwd = args.cwd
+    if args.verbose:
+        env.append("NCCL_DEBUG=INFO")
+    env.append(f"NCCL_HOST_IP={master_host}")
+    env.append(f"NCCL_PORT={master_port}")
+    env.append(f"MLX_WORLD_SIZE={world_size}")
+
+    log(args.verbose, "Running", shlex.join(command))
+
+    _launch_with_io(
+        RemoteProcess,
+        [
+            (
+                (
+                    rank,
+                    h.ssh_hostname,
+                    args.python,
+                    cwd,
+                    {},
+                    env + [f"CUDA_VISIBLE_DEVICES={rank % args.repeat_hosts}"],
+                    command,
+                ),
+                {},
+            )
+            for rank, h in enumerate(hosts)
+        ],
+        args.verbose,
+    )
+
+
+def launch_jaccl(parser, hosts, args, command):
+    if not hosts[0].ips:
+        raise ValueError("Rank 0 should have an IP reachable from all other ranks")
+
+    have_rdmas = all(len(h.rdma) == len(hosts) for h in hosts)
+    have_nulls = all(h.rdma[i] is None for i, h in enumerate(hosts))
+    if not have_rdmas or not have_nulls:
+        raise ValueError("Malformed hostfile for jaccl backend")
+
+    coordinator = hosts[0].ips[0]
+    env = args.env
+    cwd = args.cwd
+    env.append(f"MLX_JACCL_COORDINATOR={coordinator}:{args.starting_port}")
+    files = {"MLX_IBV_DEVICES": json.dumps([h.rdma for h in hosts])}
+
+    log(args.verbose, "Running", shlex.join(command))
+
+    _launch_with_io(
+        RemoteProcess,
+        [
+            ((rank, h.ssh_hostname, args.python, cwd, files, env, command), {})
+            for rank, h in enumerate(hosts)
+        ],
+        args.verbose,
+    )
+
+
+def get_mpi_libname():
+    try:
+        ompi_info = run(["which", "ompi_info"], check=True, capture_output=True)
+        ompi_info = ompi_info.stdout.strip().decode()
+
+        if platform.system() == "Darwin":
+            otool_output = run(
+                ["otool", "-L", ompi_info], check=True, capture_output=True
+            )
+        else:
+            otool_output = run(["ldd", ompi_info], check=True, capture_output=True)
+        otool_output = otool_output.stdout.decode()
+
+        # StopIteration if not found
+        libmpi_line = next(
+            filter(lambda line: "libmpi" in line, otool_output.splitlines())
+        )
+        return libmpi_line.strip().split()[0].removeprefix("@rpath/")
+    except:
+        return None
+
+
+def launch_mpi(parser, hosts, args, command):
+    mpirun = run(["which", "mpirun"], check=True, capture_output=True)
+    mpirun = mpirun.stdout.strip().decode()
+
+    # Compatibility with homebrew and pip installs
+    mpi_libname = get_mpi_libname()
+    if mpi_libname is not None:
+        dyld = Path(mpirun).parent.parent / "lib"
+        args.env = [
+            f"DYLD_LIBRARY_PATH={str(dyld)}",
+            f"MLX_MPI_LIBNAME={mpi_libname}",
+        ] + args.env
+
+    log(args.verbose, f"Using '{mpirun}'")
+    with tempfile.NamedTemporaryFile(mode="w") as f:
+        hosts = Counter((h.ssh_hostname for h in hosts))
+        for h, n in hosts.items():
+            print(f"{h} slots={n}", file=f)
+        f.flush()
+
+        cmd = [
+            mpirun,
+            "--output",
+            ":raw",  # do not line buffer output
+            "--hostfile",
+            f.name,
+            *(["-cwd", args.cwd] if args.cwd else []),
+            *sum((["-x", e] for e in args.env), []),
+            *sum([shlex.split(arg) for arg in args.mpi_arg], []),
+            "--",
+            *command,
+        ]
+        log(args.verbose, "Running", " ".join(cmd))
+        try:
+            run(cmd)
+        except KeyboardInterrupt:
+            pass
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Launch an MLX distributed program")
+    parser.add_argument(
+        "--print-python",
+        action="store_true",
+        help="Print the path to the current python executable and exit",
+    )
+    parser.add_argument(
+        "--verbose", action="store_true", help="Print debug messages in stdout"
+    )
+    parser.add_argument(
+        "--hosts", default="127.0.0.1", help="A comma separated list of hosts"
+    )
+    parser.add_argument(
+        "--repeat-hosts",
+        "-n",
+        type=positive_number,
+        default=1,
+        help="Repeat each host a given number of times",
+    )
+    parser.add_argument("--hostfile", help="The file containing the hosts")
+    parser.add_argument(
+        "--backend",
+        choices=["ring", "mpi", "nccl", "jaccl"],
+        default="nccl" if mx.cuda.is_available() else "ring",
+        help="Which distributed backend to launch",
+    )
+    parser.add_argument(
+        "--env",
+        action="append",
+        default=[],
+        help="Set environment variables for the jobs",
+    )
+    parser.add_argument(
+        "--mpi-arg",
+        action="append",
+        default=[],
+        help="Arguments to pass directly to mpirun",
+    )
+    parser.add_argument(
+        "--connections-per-ip",
+        default=1,
+        type=int,
+        help="How many connections per ip to use for the ring backend",
+    )
+    parser.add_argument(
+        "--starting-port",
+        "-p",
+        type=int,
+        default=32323,
+        help="For the ring backend listen on this port increasing by 1 per rank and IP",
+    )
+    parser.add_argument(
+        "--cwd", help="Set the working directory on each node to the provided one"
+    )
+    parser.add_argument(
+        "--nccl-port",
+        type=int,
+        default=12345,
+        help="The port to use for the NCCL communication (only for nccl backend)",
+    )
+    parser.add_argument(
+        "--no-verify-script",
+        action="store_false",
+        dest="verify_script",
+        help="Do not verify that the script exists",
+    )
+    parser.add_argument(
+        "--python", default=sys.executable, help="Use this python on the remote hosts"
+    )
+
+    args, rest = parser.parse_known_args()
+
+    if args.print_python:
+        print(args.python)
+        return
+
+    if len(rest) == 0:
+        parser.error("No script is provided")
+    if rest[0] == "--":
+        rest.pop(0)
+
+    # Try to extract a list of hosts and corresponding ips
+    if args.hostfile is not None:
+        hosts = parse_hostfile(parser, args.hostfile)
+    else:
+        hosts = parse_hostlist(parser, args.hosts, args.repeat_hosts)
+
+    # Check if the script is a file and convert it to a full path
+    if (script := Path(rest[0])).exists() and script.is_file():
+        rest[0:1] = [args.python, str(script.resolve())]
+    elif (command := shutil.which(rest[0])) is not None:
+        rest[0] = command
+    elif args.verify_script:
+        raise ValueError(f"Invalid script or command {rest[0]}")
+
+    # Launch
+    if args.backend == "ring":
+        launch_ring(parser, hosts, args, rest)
+    if args.backend == "mpi":
+        launch_mpi(parser, hosts, args, rest)
+    if args.backend == "nccl":
+        launch_nccl(parser, hosts, args, rest)
+    if args.backend == "jaccl":
+        launch_jaccl(parser, hosts, args, rest)

python/mlx/distributed_run.py

@@ -1,909 +0,0 @@
-# Copyright © 2025 Apple Inc.
-
-import argparse
-import base64
-import ipaddress
-import json
-import os
-import platform
-import shlex
-import shutil
-import sys
-import tempfile
-import threading
-import time
-from collections import Counter
-from dataclasses import dataclass
-from pathlib import Path
-from queue import Empty as QueueEmpty
-from queue import Queue
-from select import select
-from subprocess import PIPE, Popen, run
-from typing import Optional
-
-import mlx.core as mx
-
-
-@dataclass
-class Host:
-    rank: int
-    ssh_hostname: str
-    ips: list[str]
-
-
-@dataclass
-class ThunderboltPort:
-    iface: str
-    uuid: str
-    connected_to: Optional[str]
-
-
-@dataclass
-class ThunderboltHost:
-    name: str
-    ports: list[ThunderboltPort]
-
-
-def parse_hardware_ports(ports_string):
-    ports = {}
-    port_name = None
-    for l in ports_string.decode("utf-8").split("\n"):
-        if l.startswith("Hardware Port:"):
-            port_name = l.strip()[15:]
-        elif l.startswith("Device:"):
-            ports[port_name] = l.strip()[8:]
-            port_name = None
-    return ports
-
-
-def get_num_nvidia_gpus():
-    result = run(["nvidia-smi", "-L"], capture_output=True, text=True, check=True)
-    return len(result.stdout.strip().split("\n"))
-
-
-def extract_rings(hosts, index):
-    def usable_port(i, j, used_ports):
-        return (i, j) not in used_ports and hosts[i].ports[j].connected_to is not None
-
-    def dfs(start_node, node, path, visited, used_ports):
-        path.append(node)
-        visited.add(node)
-        for j, p in enumerate(hosts[node].ports):
-            if not usable_port(node, j, used_ports):
-                continue
-            next_node, _ = index[p.connected_to]
-            if next_node == start_node:
-                yield path[:]
-            if next_node not in visited:
-                yield from dfs(start_node, next_node, path, visited, used_ports)
-        path.pop()
-        visited.remove(node)
-
-    # Concretize maps the found cycle to real thunderbolt ports. It also adds
-    # those ports to the used set so next cycles can't use them again.
-    def concretize(cycle, used_ports):
-        concrete_path = []
-        for n1, n2 in zip(cycle, cycle[1:] + cycle[:1]):
-            for j, p in enumerate(hosts[n1].ports):
-                if not usable_port(n1, j, used_ports):
-                    continue
-                n2_hat, nj = index[p.connected_to]
-                if n2 == n2_hat:
-                    concrete_path.append(((n1, j), (n2, nj)))
-                    used_ports.add((n1, j))
-                    used_ports.add((n2, nj))
-                    break
-            if concrete_path[-1][0][0] != n1:
-                raise RuntimeError("Couldn't concretize the cycle")
-        return concrete_path
-
-    # Normalize tries to ensure that the cycles have the same direction so we can
-    # use them together. We achieve this by selecting the direction such that
-    # the smallest rank hosts connect to larger rank hosts.
-    def normalize(path):
-        small_to_large = sum(1 for p in path if p[0][0] < p[1][0])
-        if small_to_large > len(path) - small_to_large:
-            return path
-        else:
-            return [(p[1], p[0]) for p in path]
-
-    rings = []
-    used_ports = set()
-    for start_node in range(len(hosts)):
-        while True:
-            ring = []
-            for r in dfs(start_node, start_node, [], set(), used_ports):
-                if len(r) > len(ring):
-                    ring = r
-                # Break early since we won't find a bigger ring no matter what
-                if len(ring) == len(hosts):
-                    break
-            if not ring:
-                break
-            try:
-                rings.append(normalize(concretize(ring, used_ports)))
-            except RuntimeError:
-                if len(rings) > 0:
-                    return rings
-                raise
-
-    return rings
-
-
-def positive_number(x):
-    x = int(x)
-    if x <= 0:
-        raise ValueError("Number should be positive")
-    return x
-
-
-def log(verbose, *args, **kwargs):
-    if not verbose:
-        return
-    print("\033[32m[INFO]", *args, "\033[0m", **kwargs)
-
-
-def log_warning(*args, **kwargs):
-    kwargs["file"] = sys.stderr
-    print("\033[33m[WARN]", *args, "\033[0m", **kwargs)
-
-
-def log_error(*args, **kwargs):
-    kwargs["file"] = sys.stderr
-    print("\033[31m[ERROR]", *args, "\033[0m", **kwargs)
-
-
-def parse_hostfile(parser, hostfile):
-    """Parse the json hostfile that contains both the hostnames to ssh into and
-    the ips to communicate over when using the ring backend.
-
-    Example:
-
-        [
-            {"ssh": "hostname1", "ips": ["123.123.123.1"]},
-            {"ssh": "hostname2", "ips": ["123.123.123.2"]},
-            ...
-            {"ssh": "hostnameN", "ips": ["123.123.123.N"]},
-        ]
-
-    Args:
-        hostfile (str): The path to the json file containing the host
-            information
-    """
-    hostfile = Path(hostfile)
-    if not hostfile.exists():
-        parser.error(f"Hostfile {str(hostfile)} doesn't exist")
-
-    try:
-        hosts = []
-        with open(hostfile) as f:
-            for i, h in enumerate(json.load(f)):
-                hosts.append(Host(i, h["ssh"], h.get("ips", [])))
-        return hosts
-    except Exception as e:
-        parser.error(f"Failed to parse hostfile {str(hostfile)} ({str(e)})")
-
-
-def parse_hostlist(parser, hostlist, repeats):
-    hosts = []
-    for i, h in enumerate(hostlist.split(",")):
-        if h == "":
-            raise ValueError("Hostname cannot be empty")
-        try:
-            ipaddress.ip_address(h)
-            ips = [h]
-        except ValueError:
-            ips = []
-        for i in range(repeats):
-            hosts.append(Host(i, h, ips))
-    return hosts
-
-
-def make_monitor_script(rank, hostfile, cwd, env, command, verbose):
-    # Imports that are used throughout
-    script = ""
-    script += "import os\n"
-    script += "import sys\n"
-    script += "import tempfile\n"
-    script += "from pathlib import Path\n"
-
-    # Write the PID to a file so we can kill the process if needed
-    script += "_, pidfile = tempfile.mkstemp() \n"
-    script += "open(pidfile, 'w').write(str(os.getpid()))\n"
-    script += "print(pidfile, flush=True)\n"
-
-    # Change the working directory if one was requested. Otherwise attempt to
-    # change to the current one but don't fail if it wasn't possible.
-    d = cwd or os.getcwd()
-    script += f"if Path({repr(d)}).exists():\n"
-    script += f"    os.chdir({repr(d)})\n"
-    if cwd is not None:
-        script += "else:\n"
-        script += (
-            f"    print('Failed to change directory to', {repr(d)}, file=sys.stderr)\n"
-        )
-        script += f"    sys.exit(1)\n"
-
-    # Add the environment variables that were given to us
-    script += "env = dict(os.environ)\n"
-    for e in env:
-        key, *value = e.split("=", maxsplit=1)
-        value = shlex.quote(value[0]) if len(value) > 0 else ""
-        if not all(c.isalnum() or c == "_" for c in key):
-            log_warning(f"'{e}' is an invalid environment variable so it is ignored")
-            continue
-        script += f"env[{repr(key)}] = {repr(value)}\n"
-
-    # Add the environment variables to enable the ring distributed backend
-    if hostfile != "":
-        script += "_, hostfile = tempfile.mkstemp()\n"
-        script += "with open(hostfile, 'w') as f:\n"
-        script += f"    f.write({repr(hostfile)})\n"
-        if verbose:
-            script += "env['MLX_RING_VERBOSE'] = '1'\n"
-        script += "env['MLX_HOSTFILE'] = hostfile\n"
-        script += f"env['MLX_RANK'] = '{rank}'\n"
-        script += "\n"
-
-    # Replace the process with the script
-    script += f"command = [{','.join(map(repr, command))}]\n"
-    script += "os.execve(command[0], command, env)\n"
-
-    return script
-
-
-def launch_ring(parser, hosts, args, command):
-    stop = False
-    exit_codes = [None] * len(hosts)
-
-    def node_thread(rank, host, hostfile, input_queue):
-        is_local = host == "127.0.0.1"
-        script = make_monitor_script(
-            rank, hostfile, args.cwd, args.env, command, args.verbose
-        )
-        script_b64 = base64.b64encode(script.encode()).decode()
-        cmd = f'{sys.executable} -c "import base64; exec(base64.b64decode(\\"{script_b64}\\"));"'
-        if not is_local:
-            cmd = f"ssh {host} '{cmd}'"
-        p = Popen(
-            cmd,
-            shell=True,
-            stdin=PIPE,
-            stdout=PIPE,
-            stderr=PIPE,
-        )
-        os.set_blocking(p.stdout.fileno(), False)
-        os.set_blocking(p.stderr.fileno(), False)
-        os.set_blocking(p.stdin.fileno(), False)
-
-        # Repeat the stdout and stderr to the local machine
-        to_read = [p.stdout.fileno(), p.stderr.fileno()]
-        to_write = [p.stdin.fileno(), sys.stdout.fileno(), sys.stderr.fileno()]
-        pidfile = ""
-        stdin_buffer = b""
-        stdout_buffer = b""
-        stderr_buffer = b""
-        while p.poll() is None:
-            try:
-                stdin_buffer += input_queue.get_nowait()
-            except QueueEmpty:
-                pass
-            rlist, wlist, _ = select(to_read, to_write, [], 1.0)
-            for fd in rlist:
-                msg = os.read(fd, 8192).decode(errors="ignore")
-
-                # Fetch the PID file first if we haven't already
-                if pidfile == "":
-                    pidfile, *msg = msg.split("\n", maxsplit=1)
-                    msg = msg[0] if msg else ""
-
-                is_stdout = fd == p.stdout.fileno()
-                if is_stdout:
-                    stdout_buffer += msg.encode()
-                else:
-                    stderr_buffer += msg.encode()
-            for fd in wlist:
-                if fd == p.stdin.fileno() and len(stdin_buffer) > 0:
-                    n = os.write(fd, stdin_buffer)
-                    stdin_buffer = stdin_buffer[n:]
-                elif fd == sys.stdout.fileno() and len(stdout_buffer) > 0:
-                    n = os.write(fd, stdout_buffer)
-                    stdout_buffer = stdout_buffer[n:]
-                elif fd == sys.stderr.fileno() and len(stderr_buffer) > 0:
-                    n = os.write(fd, stderr_buffer)
-                    stderr_buffer = stderr_buffer[n:]
-            if stop:
-                p.terminate()
-                break
-        p.wait()
-        exit_codes[rank] = p.returncode
-
-        # Kill the remote program if possible
-        cmd = ""
-        cmd += f"pid=$(cat {pidfile}); "
-        cmd += "if ps -p $pid >/dev/null; then "
-        cmd += "    kill $pid; "
-        cmd += "    echo 1; "
-        cmd += "else "
-        cmd += "    echo 0; "
-        cmd += "fi; "
-        cmd += f"rm {pidfile}"
-        if not is_local:
-            cmd = f"ssh {host} '{cmd}'"
-        c = run(cmd, check=True, shell=True, capture_output=True, text=True)
-        if c.stdout.strip() == "1":
-            log_warning(f"Node with rank {rank} was killed")
-        elif p.returncode != 0:
-            log_warning(f"Node with rank {rank} exited with code {p.returncode}")
-        else:
-            log(args.verbose, f"Node with rank {rank} completed")
-
-    if all(len(h.ips) == 0 for h in hosts):
-        parser.error(
-            "The ring backend requires IPs to be provided instead of hostnames"
-        )
-
-    port = args.starting_port
-    ring_hosts = []
-    for h in hosts:
-        node = []
-        for ip in h.ips:
-            for i in range(args.connections_per_ip):
-                node.append(f"{ip}:{port}")
-                port += 1
-        ring_hosts.append(node)
-    hostfile = json.dumps(ring_hosts) if len(ring_hosts) > 1 else ""
-
-    log(args.verbose, "Running", shlex.join(command))
-
-    input_queues = []
-    threads = []
-    for i, h in enumerate(hosts):
-        if i + 1 == len(hosts):
-            time.sleep(1.0)
-        input_queues.append(Queue())
-        t = threading.Thread(
-            target=node_thread, args=(i, h.ssh_hostname, hostfile, input_queues[-1])
-        )
-        t.start()
-        threads.append(t)
-
-    os.set_blocking(sys.stdin.fileno(), False)
-    while not stop:
-        rlist, _, _ = select([sys.stdin.fileno()], [], [], 1.0)
-        for fd in rlist:
-            stdin_buffer = os.read(fd, 8192)
-            for q in input_queues:
-                q.put(stdin_buffer)
-        if any(t.is_alive() for t in threads):
-            for i, t in enumerate(threads):
-                if not t.is_alive():
-                    if exit_codes[i] != 0:
-                        stop = True
-                        break
-        else:
-            break
-    for t in threads:
-        t.join()
-
-
-def get_mpi_libname():
-    try:
-        ompi_info = run(["which", "ompi_info"], check=True, capture_output=True)
-        ompi_info = ompi_info.stdout.strip().decode()
-
-        if platform.system() == "Darwin":
-            otool_output = run(
-                ["otool", "-L", ompi_info], check=True, capture_output=True
-            )
-        else:
-            otool_output = run(["ldd", ompi_info], check=True, capture_output=True)
-        otool_output = otool_output.stdout.decode()
-
-        # StopIteration if not found
-        libmpi_line = next(
-            filter(lambda line: "libmpi" in line, otool_output.splitlines())
-        )
-        return libmpi_line.strip().split()[0].removeprefix("@rpath/")
-    except:
-        return None
-
-
-def launch_mpi(parser, hosts, args, command):
-    mpirun = run(["which", "mpirun"], check=True, capture_output=True)
-    mpirun = mpirun.stdout.strip().decode()
-
-    # Compatibility with homebrew and pip installs
-    mpi_libname = get_mpi_libname()
-    if mpi_libname is not None:
-        dyld = Path(mpirun).parent.parent / "lib"
-        args.env = [
-            f"DYLD_LIBRARY_PATH={str(dyld)}",
-            f"MLX_MPI_LIBNAME={mpi_libname}",
-        ] + args.env
-
-    log(args.verbose, f"Using '{mpirun}'")
-    with tempfile.NamedTemporaryFile(mode="w") as f:
-        hosts = Counter((h.ssh_hostname for h in hosts))
-        for h, n in hosts.items():
-            print(f"{h} slots={n}", file=f)
-        f.flush()
-
-        cmd = [
-            mpirun,
-            "--output",
-            ":raw",  # do not line buffer output
-            "--hostfile",
-            f.name,
-            *(["-cwd", args.cwd] if args.cwd else []),
-            *sum((["-x", e] for e in args.env), []),
-            *sum([shlex.split(arg) for arg in args.mpi_arg], []),
-            "--",
-            *command,
-        ]
-        log(args.verbose, "Running", " ".join(cmd))
-        try:
-            run(cmd)
-        except KeyboardInterrupt:
-            pass
-
-
-def launch_nccl(parser, hosts, args, command):
-    master_host = hosts[0].ips[0]
-
-    if master_host != "127.0.0.1":
-        raise ValueError("The NCCL backend only supports localhost for now.")
-    master_port = args.nccl_port
-    world_size = len(hosts)
-
-    base_env = os.environ.copy()
-    base_env.update(
-        {
-            "NCCL_DEBUG": base_env.get(
-                "NCCL_DEBUG", "INFO" if args.verbose else "DEBUG"
-            ),
-            "NCCL_SOCKET_IFNAME": "lo",  # Use loopback for local communication
-            "NCCL_HOST_IP": master_host,
-            "NCCL_PORT": str(master_port),
-            "MLX_WORLD_SIZE": str(world_size),
-        }
-    )
-    procs = []
-    num_gpus = get_num_nvidia_gpus()
-    if num_gpus == 0:
-        raise RuntimeError("Cannot run NCCL backend with no GPUs.")
-    if args.repeat_hosts > num_gpus:
-        raise RuntimeError("NCCL requires a separate GPU per process.")
-
-    try:
-        for rank in range(world_size):
-            env = base_env.copy()
-            mlx_rank = str(rank % args.repeat_hosts)
-            env["MLX_RANK"] = mlx_rank
-            env["CUDA_VISIBLE_DEVICES"] = mlx_rank
-            p = Popen(command, env=env)
-            procs.append(p)
-
-        for p in procs:
-            ret = p.wait()
-            if ret != 0:
-                raise RuntimeError(f"Rank process exited with {ret}")
-
-    except (RuntimeError, KeyboardInterrupt) as err:
-        for p in procs:
-            if p.poll() is None:
-                try:
-                    p.kill()
-                except Exception:
-                    pass
-        raise
-
-
-def check_ssh_connections(hosts):
-    results = [False] * len(hosts)
-
-    def _check(hostname, i):
-        result = run(
-            [
-                "ssh",
-                "-o",
-                "BatchMode=yes",
-                "-o",
-                "ConnectTimeout=5",
-                hostname,
-                "echo",
-                "success",
-            ],
-            stdout=PIPE,
-            stderr=PIPE,
-        )
-        results[i] = result.returncode == 0
-
-    threads = [
-        threading.Thread(target=_check, args=(h.ssh_hostname, i))
-        for i, h in enumerate(hosts)
-    ]
-    for t in threads:
-        t.start()
-    for t in threads:
-        t.join()
-
-    if not all(results):
-        log_error("Could not ssh to the following hosts:")
-        for i, h in enumerate(hosts):
-            if not results[i]:
-                log_error("  - ", h.ssh_hostname)
-        log_error()
-        log_error("Maybe they are not set-up for password-less ssh?")
-        sys.exit(1)
-
-
-def prepare_tb_ring(args, hosts):
-    log(
-        args.verbose,
-        f"Preparing a thunderbolt ring for {', '.join(h.ssh_hostname for h in hosts)}",
-    )
-
-    # Check that we can ssh
-    check_ssh_connections(hosts)
-    if args.auto_setup and args.verbose:
-        log_warning(
-            "--auto-setup is requested which requires password-less sudo",
-            "on the remote hosts",
-        )
-
-    # Extract the current connectivity from the remote hosts
-    thunderbolt_connections = []
-    for h in hosts:
-        log(args.verbose, "Getting connectivity from", h.ssh_hostname)
-        thunderbolt_connections.append(
-            json.loads(
-                run(
-                    [
-                        "ssh",
-                        h.ssh_hostname,
-                        "system_profiler",
-                        "SPThunderboltDataType",
-                        "-json",
-                    ],
-                    capture_output=True,
-                ).stdout
-            )
-        )
-    interface_maps = []
-    for h in hosts:
-        log(args.verbose, "Getting interface names from", h.ssh_hostname)
-        interface_maps.append(
-            parse_hardware_ports(
-                run(
-                    [
-                        "ssh",
-                        h.ssh_hostname,
-                        "networksetup",
-                        "-listallhardwareports",
-                    ],
-                    capture_output=True,
-                ).stdout
-            )
-        )
-
-    # Parse the connectivity into some simple dataclasses
-    tb_hosts = []
-    for c, iface_map in zip(thunderbolt_connections, interface_maps):
-        name = ""
-        ports = []
-        for t in c["SPThunderboltDataType"]:
-            uuid = t.get("domain_uuid_key")
-            if uuid is None:
-                continue
-            name = t["device_name_key"]
-            tag = t["receptacle_1_tag"]["receptacle_id_key"]
-            items = t.get("_items", [])
-            connected_items = [item for item in items if "domain_uuid_key" in item]
-            connected_to = (
-                connected_items[0]["domain_uuid_key"] if connected_items else None
-            )
-            iface = iface_map[f"Thunderbolt {tag}"]
-            ports.append(ThunderboltPort(iface, uuid, connected_to))
-        tb_hosts.append(ThunderboltHost(name, sorted(ports, key=lambda x: x.iface)))
-
-    # Create a reverse index to be able to map uuids to (host, port) quickly
-    uuid_reverse_index = {}
-    for i, h in enumerate(tb_hosts):
-        for j, p in enumerate(h.ports):
-            uuid_reverse_index[p.uuid] = (i, j)
-
-    # Find the rings by simply walking and marking visited (host, port) tuples
-    # and keeping the largest rings greedily.
-    log(args.verbose, "Extracting rings from the parsed connectivity")
-    rings = extract_rings(tb_hosts, uuid_reverse_index)
-
-    # Just output a DOT graphical representation of the found rings
-    if args.dot:
-        names = []
-        for i in range(len(tb_hosts)):
-            n = ""
-            j = i
-            while True:
-                n += chr(97 + j % 26)
-                j //= 26
-                if j == 0:
-                    break
-            names.append(n)
-
-        print("graph G {")
-        print("  node [shape=rectangle];")
-        for i, h in enumerate(hosts):
-            print(f'  {names[i]} [label="{h.ssh_hostname}"];')
-        for r in rings:
-            for (i, _), (j, _) in r:
-                print(f"  {names[i]} -- {names[j]};")
-        print("}")
-        return
-
-    # Assign IPs to each interface such that the interfaces can communicate
-    ips = {}
-    pairs = {}
-    expecting = set()
-    ip0 = 0
-    ip1 = 0
-    netmask = "255.255.255.252"
-    for r in rings:
-        for a, b in r:
-            ips[a] = f"192.168.{ip0}.{ip1 + 1}"
-            ips[b] = f"192.168.{ip0}.{ip1 + 2}"
-            pairs[a] = b
-            pairs[b] = a
-            expecting.add(b)
-            ip1 += 4
-            if ip1 > 255:
-                ip0 += 1
-                ip1 = 0
-            if ip0 > 255:
-                raise ValueError("Ran out of available local IPs for the ring")
-
-    # Extract the host order from the first ring
-    hostmap = dict((r[0][0], r[1][0]) for r in rings[0])
-    first_host = min(hostmap.keys())
-    order = [first_host]
-    while hostmap[order[-1]] != first_host:
-        order.append(hostmap[order[-1]])
-
-    # Create the hostfile
-    hostfile = []
-    for i in order:
-        h = hosts[i]
-        host = {
-            "ssh": h.ssh_hostname,
-            "ips": [
-                ips[i, j]
-                for j, p in enumerate(tb_hosts[i].ports)
-                if (i, j) in expecting
-            ],
-        }
-        hostfile.append(host)
-
-    if not args.hostfile_only:
-        for i, h in enumerate(hosts):
-            command = ""
-            command += "sudo ifconfig bridge0 down\n"
-            for j, p in enumerate(tb_hosts[i].ports):
-                if (i, j) not in ips:
-                    continue
-                iface = p.iface
-                ip = ips[i, j]
-                peer = ips[pairs[i, j]]
-                command += f"sudo ifconfig {iface} inet {ip} netmask {netmask}\n"
-                command += f"sudo route change {peer} -interface {iface}\n"
-            if args.auto_setup:
-                print(f"Running auto setup for {h.ssh_hostname}")
-                command = command.strip().replace("\n", " && ")
-                command = ["ssh", h.ssh_hostname, command]
-                log(args.verbose, shlex.join(command))
-                run(command)
-            else:
-                msg = f"Setup for {h.ssh_hostname}"
-                print(msg)
-                print("=" * len(msg))
-                print(command)
-                input("Enter to continue")
-            print()
-
-    if args.output_hostfile:
-        with open(args.output_hostfile, "w") as f:
-            json.dump(hostfile, f, indent=4)
-    else:
-        print("Hostfile")
-        print("========")
-        print(json.dumps(hostfile, indent=4))
-
-
-def prepare_hostfile(args, hosts):
-    log(
-        args.verbose,
-        f"Preparing an ethernet hostfile for {', '.join(h.ssh_hostname for h in hosts)}",
-    )
-
-    # Check that we can ssh
-    check_ssh_connections(hosts)
-
-    # Get the ips for each host
-    for h in hosts:
-        log(args.verbose, "Getting the ip from", h.ssh_hostname)
-        h.ips.append(
-            run(
-                ["ssh", h.ssh_hostname, "ipconfig", "getifaddr", "en0"],
-                capture_output=True,
-                text=True,
-            ).stdout.strip()
-        )
-
-    hostfile = []
-    for h in hosts:
-        hostfile.append(dict(ssh=h.ssh_hostname, ips=h.ips))
-
-    if args.output_hostfile:
-        with open(args.output_hostfile, "w") as f:
-            json.dump(hostfile, f, indent=4)
-    else:
-        print("Hostfile")
-        print("========")
-        print(json.dumps(hostfile, indent=4))
-
-
-def distributed_config():
-    parser = argparse.ArgumentParser(
-        description="Configure remote machines for use with MLX distributed"
-    )
-    parser.add_argument(
-        "--verbose", action="store_true", help="Print debug messages in stdout"
-    )
-    parser.add_argument(
-        "--backend",
-        choices=["ring", "mpi", "nccl"],
-        default="nccl" if mx.cuda.is_available() else "ring",
-        help="Which distributed backend to configure",
-    )
-    parser.add_argument(
-        "--over",
-        choices=["thunderbolt", "ethernet"],
-        default="thunderbolt",
-        help="What type of connectivity to configure",
-    )
-    parser.add_argument(
-        "--hosts", default="127.0.0.1", help="A comma separated list of hosts"
-    )
-    parser.add_argument("--hostfile", help="The file containing the hosts")
-    parser.add_argument(
-        "--dot", action="store_true", help="Output the topology in DOT format and exit"
-    )
-    parser.add_argument(
-        "--hostfile-only", action="store_true", help="If set only compute the hostfile"
-    )
-    parser.add_argument(
-        "--output-hostfile", help="If provided, save the hostfile to this path"
-    )
-    parser.add_argument(
-        "--auto-setup",
-        action="store_true",
-        help="If set we will attempt to automatically configure the machines via ssh",
-    )
-    args = parser.parse_args()
-
-    if args.backend == "mpi" and args.over == "thunderbolt":
-        raise ValueError(
-            (
-                "The configuration of MPI over thunderbolt is "
-                "not supported yet by mlx.distributed_config"
-            )
-        )
-
-    if args.hostfile is not None:
-        hosts = parse_hostfile(parser, args.hostfile)
-    else:
-        hosts = parse_hostlist(parser, args.hosts, 1)
-
-    if args.over == "thunderbolt":
-        prepare_tb_ring(args, hosts)
-    else:
-        prepare_hostfile(args, hosts)
-
-
-def main():
-    parser = argparse.ArgumentParser(description="Launch an MLX distributed program")
-    parser.add_argument(
-        "--print-python",
-        action="store_true",
-        help="Print the path to the current python executable and exit",
-    )
-    parser.add_argument(
-        "--verbose", action="store_true", help="Print debug messages in stdout"
-    )
-    parser.add_argument(
-        "--hosts", default="127.0.0.1", help="A comma separated list of hosts"
-    )
-    parser.add_argument(
-        "--repeat-hosts",
-        "-n",
-        type=positive_number,
-        default=1,
-        help="Repeat each host a given number of times",
-    )
-    parser.add_argument("--hostfile", help="The file containing the hosts")
-    parser.add_argument(
-        "--backend",
-        choices=["ring", "mpi", "nccl"],
-        default="nccl" if mx.cuda.is_available() else "ring",
-        help="Which distributed backend to launch",
-    )
-    parser.add_argument(
-        "--env",
-        action="append",
-        default=[],
-        help="Set environment variables for the jobs",
-    )
-    parser.add_argument(
-        "--mpi-arg",
-        action="append",
-        default=[],
-        help="Arguments to pass directly to mpirun",
-    )
-    parser.add_argument(
-        "--connections-per-ip",
-        default=1,
-        type=int,
-        help="How many connections per ip to use for the ring backend",
-    )
-    parser.add_argument(
-        "--starting-port",
-        "-p",
-        type=int,
-        default=5000,
-        help="For the ring backend listen on this port increasing by 1 per rank and IP",
-    )
-    parser.add_argument(
-        "--cwd", help="Set the working directory on each node to the provided one"
-    )
-    parser.add_argument(
-        "--nccl-port",
-        type=int,
-        default=12345,
-        help="The port to use for the NCCL communication (only for nccl backend)",
-    )
-
-    args, rest = parser.parse_known_args()
-
-    if args.print_python:
-        print(sys.executable)
-        return
-
-    if len(rest) == 0:
-        parser.error("No script is provided")
-    if rest[0] == "--":
-        rest.pop(0)
-
-    # Try to extract a list of hosts and corresponding ips
-    if args.hostfile is not None:
-        hosts = parse_hostfile(parser, args.hostfile)
-    else:
-        hosts = parse_hostlist(parser, args.hosts, args.repeat_hosts)
-
-    # Check if the script is a file and convert it to a full path
-    if (script := Path(rest[0])).exists():
-        rest[0:1] = [sys.executable, str(script.resolve())]
-    elif (command := shutil.which(rest[0])) is not None:
-        rest[0] = command
-    else:
-        raise ValueError(f"Invalid script or command {rest[0]}")
-
-    # Launch
-    if args.backend == "ring":
-        launch_ring(parser, hosts, args, rest)
-    if args.backend == "mpi":
-        launch_mpi(parser, hosts, args, rest)
-    if args.backend == "nccl":
-        launch_nccl(parser, hosts, args, rest)
-
-
-if __name__ == "__main__":
-    main()

python/scripts/repair_cuda.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 auditwheel repair dist/* \
-  --plat manylinux_2_35_x86_64 \
+  --plat manylinux_2_35_${1} \
   --exclude libcublas* \
   --exclude libnvrtc* \
   --exclude libcuda* \

python/src/distributed.cpp

@@ -52,9 +52,25 @@ void init_distributed(nb::module_& parent_module) {
 
   m.def(
       "is_available",
-      &mx::distributed::is_available,
+      [](const std::string& backend) {
+        return mx::distributed::is_available(backend);
+      },
+      "backend"_a = "any",
+      nb::sig("def is_available(backend: str = 'any') -> bool"),
       R"pbdoc(
       Check if a communication backend is available.
+
+      Note, this function returns whether MLX has the capability of
+      instantiating that distributed backend not whether it is possible to
+      create a communication group. For that purpose one should use
+      ``init(strict=True)``.
+
+      Args:
+        backend (str, optional): The name of the backend to check for availability.
+          It takes the same values as :func:`init()`. Default: ``"any"``.
+
+      Returns:
+        bool: Whether the distributed backend is available.
       )pbdoc");
 
   m.def(
@@ -79,10 +95,10 @@ void init_distributed(nb::module_& parent_module) {
             in case ``mx.distributed.is_available()`` returns False otherwise
             it throws a runtime error. Default: ``False``
           backend (str, optional): Which distributed backend to initialize.
-            Possible values ``mpi``, ``ring``, ``nccl``, ``any``. If set to ``any`` all
+            Possible values ``mpi``, ``ring``, ``nccl``, ``jaccl``, ``any``. If
-            available backends are tried and the first one that succeeds
+            set to ``any`` all available backends are tried and the first one
-            becomes the global group which will be returned in subsequent
+            that succeeds becomes the global group which will be returned in
-            calls. Default: ``any``
+            subsequent calls. Default: ``any``
 
         Returns:
           Group: The group representing all the launched processes.

python/tests/test_reduce.py

@@ -210,6 +210,14 @@ class TestReduce(mlx_tests.MLXTestCase):
                     ref = getattr(np, op)(np_arr, axis=axis)
                     self.assertTrue(np.array_equal(out, ref, equal_nan=True))
 
+    def test_long_column(self):
+        a = (np.random.randn(8192, 64) * 32).astype(np.int32)
+        b = mx.array(a)
+
+        c1 = a.sum(0)
+        c2 = b.sum(0)
+        self.assertTrue(np.all(c1 == c2))
+
 
 if __name__ == "__main__":
     mlx_tests.MLXTestRunner(failfast=True)

setup.py

@@ -7,13 +7,21 @@ import re
 import subprocess
 from functools import partial
 from pathlib import Path
-from subprocess import run
 
 from setuptools import Command, Extension, find_namespace_packages, setup
 from setuptools.command.bdist_wheel import bdist_wheel
 from setuptools.command.build_ext import build_ext
 
 
+def cuda_toolkit_major_version():
+    out = subprocess.check_output(["nvcc", "--version"], stderr=subprocess.STDOUT)
+    text = out.decode()
+    m = re.search(r"release (\d+)", text)
+    if m:
+        return int(m.group(1))
+    return None
+
+
 def get_version():
     with open("mlx/version.h", "r") as fid:
         for l in fid:
@@ -31,7 +39,7 @@ def get_version():
         version = f"{version}.dev{today.year}{today.month:02d}{today.day:02d}"
     if not pypi_release and not dev_release:
         git_hash = (
-            run(
+            subprocess.run(
                 "git rev-parse --short HEAD".split(),
                 capture_output=True,
                 check=True,
@@ -257,8 +265,8 @@ if __name__ == "__main__":
     }
     entry_points = {
         "console_scripts": [
-            "mlx.launch = mlx.distributed_run:main",
+            "mlx.launch = mlx._distributed_utils.launch:main",
-            "mlx.distributed_config = mlx.distributed_run:distributed_config",
+            "mlx.distributed_config = mlx._distributed_utils.config:main",
         ]
     }
     install_requires = []
@@ -284,7 +292,11 @@ if __name__ == "__main__":
             install_requires.append(
                 f'mlx-metal=={version}; platform_system == "Darwin"'
             )
-            extras["cuda"] = [f'mlx-cuda=={version}; platform_system == "Linux"']
+            extras["cuda"] = [f'mlx-cuda-12=={version}; platform_system == "Linux"']
+            for toolkit in [12, 13]:
+                extras[f"cuda{toolkit}"] = [
+                    f'mlx-cuda-{toolkit}=={version}; platform_system == "Linux"'
+                ]
             extras["cpu"] = [f'mlx-cpu=={version}; platform_system == "Linux"']
 
         _setup(
@@ -299,13 +311,25 @@ if __name__ == "__main__":
         if build_macos:
             name = "mlx-metal"
         elif build_cuda:
-            name = "mlx-cuda"
+            toolkit = cuda_toolkit_major_version()
+            name = f"mlx-cuda-{toolkit}"
+            if toolkit == 12:
+                install_requires += [
+                    "nvidia-cublas-cu12==12.9.*",
+                    "nvidia-cuda-nvrtc-cu12==12.9.*",
+                ]
+            elif toolkit == 13:
+                install_requires += [
+                    "nvidia-cublas-cu13",
+                    "nvidia-cuda-nvrtc-cu13",
+                ]
+            else:
+                raise ValueError(f"Unknown toolkit {toolkit}")
             install_requires += [
-                "nvidia-cublas-cu12==12.9.*",
+                f"nvidia-cudnn-cu{toolkit}==9.*",
-                "nvidia-cuda-nvrtc-cu12==12.9.*",
+                f"nvidia-nccl-cu{toolkit}",
-                "nvidia-cudnn-cu12==9.*",
-                "nvidia-nccl-cu12",
             ]
+
         else:
             name = "mlx-cpu"
         _setup(

tests/array_tests.cpp

@@ -1,5 +1,4 @@
 // Copyright © 2023 Apple Inc.
-
 #include <climits>
 
 #include "doctest/doctest.h"
@@ -608,3 +607,24 @@ TEST_CASE("test make empty array") {
   CHECK_EQ(a.size(), 0);
   CHECK_EQ(a.dtype(), bool_);
 }
+
+TEST_CASE("test make array from user buffer") {
+  int size = 4096;
+  std::vector<int> buffer(size, 0);
+
+  int count = 0;
+  auto deleter = [&count](void*) { count++; };
+
+  {
+    auto a = array(buffer.data(), Shape{size}, int32, deleter);
+    if (metal::is_available()) {
+      CHECK_EQ(buffer.data(), a.data<int>());
+    }
+    auto b = a + array(1);
+    eval(b);
+    auto expected = ones({4096});
+    CHECK(array_equal(b, expected).item<bool>());
+  }
+  // deleter should always get called
+  CHECK_EQ(count, 1);
+}