Add rudimentary barrier

mlx/distributed/CMakeLists.txt

@@ -1,8 +1,16 @@
 target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/primitives.cpp
                            ${CMAKE_CURRENT_SOURCE_DIR}/ops.cpp)
 
-if(MPI_FOUND AND MLX_BUILD_CPU)
-  add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/mpi)
-else()
-  target_sources(mlx PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/no_distributed.cpp)
+if (MLX_BUILD_CPU)
+    if (MLX_CUSTOM_DISTRIBUTED)
+      add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/sockets)
+    elseif (MPI_FOUND)
+      add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/mpi)
+    else()
+      target_sources(
+        mlx
+        PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/no_distributed.cpp
+      )
+    endif()
 endif()

mlx/distributed/distributed.h

@@ -32,6 +32,8 @@ struct Group {
    */
   Group split(int color, int key = -1);
 
+  void barrier();
+
   const std::shared_ptr<void>& raw_group() {
     return group_;
   }

mlx/distributed/mpi/mpi.cpp

@@ -71,6 +71,7 @@ struct MPIWrapper {
     LOAD_SYMBOL(MPI_Allgather, all_gather);
     LOAD_SYMBOL(MPI_Send, send);
     LOAD_SYMBOL(MPI_Recv, recv);
+    LOAD_SYMBOL(MPI_Barrier, barrier);
     LOAD_SYMBOL(MPI_Type_contiguous, mpi_type_contiguous);
     LOAD_SYMBOL(MPI_Type_commit, mpi_type_commit);
     LOAD_SYMBOL(MPI_Op_create, mpi_op_create);
@@ -195,6 +196,7 @@ struct MPIWrapper {
   int (*comm_free)(MPI_Comm*);
   int (*send)(const void*, int, MPI_Datatype, int, int, MPI_Comm);
   int (*recv)(void*, int, MPI_Datatype, int, int, MPI_Comm, MPI_Status*);
+  int (*barrier)(MPI_Comm);
 
   // Objects
   MPI_Comm comm_world_;
@@ -263,6 +265,10 @@ struct MPIGroupImpl {
     return size_;
   }
 
+  void barrier() {
+    mpi().barrier(comm_);
+  }
+
  private:
   MPI_Comm comm_;
   bool global_;
@@ -298,6 +304,11 @@ Group Group::split(int color, int key) {
   return Group(std::make_shared<MPIGroupImpl>(new_comm, false));
 }
 
+void Group::barrier() {
+  auto mpi_group = std::static_pointer_cast<MPIGroupImpl>(group_);
+  mpi_group->barrier();
+}
+
 bool is_available() {
   return mpi().is_available();
 }

mlx/distributed/no_distributed.cpp

@@ -17,6 +17,8 @@ Group Group::split(int color, int key) {
   throw std::runtime_error("Cannot split the distributed group further");
 }
 
+void Group::barrier() {}
+
 bool is_available() {
   return false;
 }

mlx/distributed/sockets/CMakeLists.txt

@@ -0,0 +1,5 @@
+target_sources(
+  mlx
+  PRIVATE
+  ${CMAKE_CURRENT_SOURCE_DIR}/sockets.cpp
+)

mlx/distributed/sockets/sockets.cpp

@@ -0,0 +1,522 @@
+// Copyright © 2024 Apple Inc.
+
+#include <arpa/inet.h>
+#include <json.hpp>
+#include <netdb.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <chrono>
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+#include <thread>
+
+#include "mlx/backend/common/copy.h"
+#include "mlx/distributed/distributed.h"
+#include "mlx/distributed/distributed_impl.h"
+#include "mlx/io/threadpool.h"
+
+#define SWITCH_TYPE(x, ...)  \
+  switch ((x).dtype()) {     \
+    case bool_: {            \
+      using T = bool;        \
+      __VA_ARGS__;           \
+    } break;                 \
+    case int8: {             \
+      using T = int8_t;      \
+      __VA_ARGS__;           \
+    } break;                 \
+    case int16: {            \
+      using T = int16_t;     \
+      __VA_ARGS__;           \
+    } break;                 \
+    case int32: {            \
+      using T = int32_t;     \
+      __VA_ARGS__;           \
+    } break;                 \
+    case int64: {            \
+      using T = int64_t;     \
+      __VA_ARGS__;           \
+    } break;                 \
+    case uint8: {            \
+      using T = uint8_t;     \
+      __VA_ARGS__;           \
+    } break;                 \
+    case uint16: {           \
+      using T = uint16_t;    \
+      __VA_ARGS__;           \
+    } break;                 \
+    case uint32: {           \
+      using T = uint32_t;    \
+      __VA_ARGS__;           \
+    } break;                 \
+    case uint64: {           \
+      using T = uint64_t;    \
+      __VA_ARGS__;           \
+    } break;                 \
+    case bfloat16: {         \
+      using T = bfloat16_t;  \
+      __VA_ARGS__;           \
+    } break;                 \
+    case float16: {          \
+      using T = float16_t;   \
+      __VA_ARGS__;           \
+    } break;                 \
+    case float32: {          \
+      using T = float;       \
+      __VA_ARGS__;           \
+    } break;                 \
+    case complex64: {        \
+      using T = complex64_t; \
+      __VA_ARGS__;           \
+    } break;                 \
+  }
+
+constexpr const size_t PACKET_SIZE = 262144;
+constexpr const int CONN_ATTEMPTS = 5;
+constexpr const int CONN_WAIT = 1000;
+
+using json = nlohmann::json;
+
+namespace mlx::core::distributed {
+
+namespace {
+
+template <typename T>
+void sum_inplace(const T* input, T* output, size_t N) {
+  while (N-- > 0) {
+    *output += *input;
+    input++;
+    output++;
+  }
+}
+
+void sum_inplace(const array& input, array& output) {
+  SWITCH_TYPE(
+      input, sum_inplace(input.data<T>(), output.data<T>(), input.size()));
+}
+
+array ensure_row_contiguous(const array& arr) {
+  if (arr.flags().row_contiguous) {
+    return arr;
+  } else {
+    array arr_copy(arr.shape(), arr.dtype(), nullptr, {});
+    copy(arr, arr_copy, CopyType::General);
+    return arr_copy;
+  }
+}
+
+struct address_t {
+  sockaddr_storage addr;
+  socklen_t len;
+
+  const sockaddr* sockaddr() {
+    return (struct sockaddr*)&addr;
+  }
+};
+
+address_t parse_address(std::string ip, 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 peer 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;
+}
+
+std::vector<address_t> load_peers() {
+  std::vector<address_t> peers;
+  std::ifstream f;
+
+  if (const char* hostfile_buf = std::getenv("MLX_HOSTFILE")) {
+    f.open(hostfile_buf);
+  } else {
+    return peers;
+  }
+
+  json hosts = json::parse(f);
+  for (auto& h : hosts) {
+    peers.push_back(std::move(parse_address(
+        h["ip"].template get<std::string>(),
+        h["port"].template get<std::string>())));
+  }
+
+  return peers;
+}
+
+struct GroupImpl {
+  GroupImpl(std::vector<address_t> peers, int rank, bool global)
+      : rank_(rank), global_(global), pool_(4), sockets_(peers.size(), -1) {
+    if (rank_ > 0 && rank_ >= peers.size()) {
+      throw std::runtime_error(
+          "Rank cannot be larger than the size of the group");
+    }
+
+    int success;
+
+    // If we are expecting anyone to connect to us
+    if (rank_ + 1 < peers.size()) {
+      // Create the socket to wait for connections from the peers
+      int sock = socket(AF_INET, SOCK_STREAM, 0);
+      if (sock < 0) {
+        std::ostringstream msg;
+        msg << "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 << "Couldn't enable reuseaddr (rank: " << rank_
+            << " 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 << "Couldn't enable reuseport (rank: " << rank_
+            << " error: " << errno << ")";
+        throw std::runtime_error(msg.str());
+      }
+
+      // Bind it to the port
+      success = bind(sock, peers[rank_].sockaddr(), peers[rank_].len);
+      if (success < 0) {
+        shutdown(sock, 2);
+        close(sock);
+        std::ostringstream msg;
+        msg << "Couldn't bind socket (rank: " << rank_ << " 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 << "Couldn't listen (error: " << errno << ")";
+        throw std::runtime_error(msg.str());
+      }
+      for (int i = 0; i < peers.size() - rank_ - 1; i++) {
+        int peer_socket = accept(sock, nullptr, nullptr);
+        if (peer_socket < 0) {
+          shutdown(sock, 2);
+          close(sock);
+          std::ostringstream msg;
+          msg << "Accept failed (error: " << errno << ")";
+          throw std::runtime_error(msg.str());
+        }
+        sockets_[peers.size() - 1 - i] = peer_socket;
+      }
+
+      // Close the listening socket
+      shutdown(sock, 2);
+      close(sock);
+    }
+
+    // Connect to the peers with smaller rank
+    for (int i = 0; i < rank_; i++) {
+      sockets_[i] = socket(AF_INET, SOCK_STREAM, 0);
+      if (sockets_[i] < 0) {
+        std::ostringstream msg;
+        msg << "Couldn't create socket (error: " << errno << ")";
+        throw std::runtime_error(msg.str());
+      }
+      for (int attempt = 0; attempt < CONN_ATTEMPTS; attempt++) {
+        if (attempt > 0) {
+          int wait = (1 << (attempt - 1)) * CONN_WAIT;
+          std::this_thread::sleep_for(std::chrono::milliseconds(wait));
+        }
+        success = connect(sockets_[i], peers[i].sockaddr(), peers[i].len);
+        if (success == 0) {
+          break;
+        }
+      }
+      if (success < 0) {
+        std::ostringstream msg;
+        msg << "Couldn't connect (rank: " << rank_ << " to: " << i
+            << " error: " << errno << ")";
+        throw std::runtime_error(msg.str());
+      }
+    }
+  }
+
+  ~GroupImpl() {
+    if (global_) {
+      for (int sock : sockets_) {
+        shutdown(sock, 2);
+        close(sock);
+      }
+    }
+  }
+
+  int rank() {
+    return rank_;
+  }
+
+  int size() {
+    return std::max(sockets_.size(), 1ul);
+  }
+
+  void send(const char* buf, size_t len, int dst) {
+    while (len > 0) {
+      ssize_t r = ::send(sockets_[dst], buf, len, 0);
+      if (r <= 0) {
+        std::ostringstream msg;
+        msg << "Send of " << len << " bytes failed (errno: " << errno << ")";
+        throw std::runtime_error(msg.str());
+      }
+      buf += r;
+      len -= r;
+    }
+  }
+
+  void recv(char* buf, size_t len, int src) {
+    while (len > 0) {
+      ssize_t r = ::recv(sockets_[src], buf, len, 0);
+      if (r <= 0) {
+        std::ostringstream msg;
+        msg << "Recv of " << len << " bytes failed (errno: " << errno << ")";
+        throw std::runtime_error(msg.str());
+      }
+      buf += r;
+      len -= r;
+    }
+  }
+
+  template <typename T>
+  void send_recv_sum(char* buf, size_t len, int peer) {
+    char recv_buffer[2 * PACKET_SIZE];
+    char* recv_buffers[2];
+    recv_buffers[0] = recv_buffer;
+    recv_buffers[1] = recv_buffer + PACKET_SIZE;
+    std::future<void> sent, received;
+    size_t n_blocks = (len + PACKET_SIZE - 1) / PACKET_SIZE;
+
+    for (size_t b = 0; b < n_blocks; b++) {
+      if (b > 0) {
+        sent.wait();
+        received.wait();
+      }
+      size_t l = std::min(len - b * PACKET_SIZE, PACKET_SIZE);
+      if (rank_ < peer) {
+        sent = send_async(buf + b * PACKET_SIZE, l, peer);
+        received = recv_async(recv_buffers[b % 2], l, peer);
+      } else {
+        received = recv_async(recv_buffers[b % 2], l, peer);
+        sent = send_async(buf + b * PACKET_SIZE, l, peer);
+      }
+      if (b > 0) {
+        sum_inplace(
+            (const T*)recv_buffers[(b - 1) % 2],
+            (T*)(buf + (b - 1) * PACKET_SIZE),
+            PACKET_SIZE / sizeof(T));
+      }
+    }
+    sent.wait();
+    received.wait();
+    size_t l = std::min(len - (n_blocks - 1) * PACKET_SIZE, PACKET_SIZE);
+    sum_inplace(
+        (const T*)recv_buffers[(n_blocks - 1) % 2],
+        (T*)(buf + (n_blocks - 1) * PACKET_SIZE),
+        l / sizeof(T));
+  }
+
+  void send_recv_sum(array& out, int peer) {
+    SWITCH_TYPE(out, send_recv_sum<T>(out.data<char>(), out.nbytes(), peer));
+  }
+
+  std::future<void> send_async(const char* buf, size_t len, int dst) {
+    return pool_.enqueue(
+        [this, buf, len, dst]() { this->send(buf, len, dst); });
+  }
+
+  std::future<void> recv_async(char* buf, size_t len, int src) {
+    return pool_.enqueue(
+        [this, buf, len, src]() { this->recv(buf, len, src); });
+  }
+
+ private:
+  int rank_;
+  bool global_;
+  ThreadPool pool_;
+  std::vector<int> sockets_;
+};
+
+} // namespace
+
+bool is_available() {
+  return true;
+}
+
+int Group::rank() {
+  return std::static_pointer_cast<GroupImpl>(group_)->rank();
+}
+
+int Group::size() {
+  return std::static_pointer_cast<GroupImpl>(group_)->size();
+}
+
+Group Group::split(int color, int key) {
+  throw std::runtime_error("Splitting not supported yet");
+}
+
+void Group::barrier() {
+  char buff[128];
+  std::memset(buff, 1, 128);
+
+  auto group = std::static_pointer_cast<GroupImpl>(raw_group());
+  int size = group->size();
+  int rank = group->rank();
+
+  for (int distance = 1; distance <= size / 2; distance *= 2) {
+    group->send_recv_sum<char>(buff, 128, rank ^ distance);
+  }
+}
+
+Group init(bool strict /* = false */) {
+  static std::shared_ptr<GroupImpl> global_group = nullptr;
+
+  if (global_group == nullptr) {
+    auto peers = load_peers();
+    int rank = 0;
+    if (const char* rank_buf = std::getenv("MLX_RANK")) {
+      rank = std::atoi(rank_buf);
+    }
+    if (peers.size() == 0) {
+      if (strict) {
+        throw std::runtime_error("Can't initialize distributed");
+      }
+    }
+    global_group = std::make_shared<GroupImpl>(std::move(peers), rank, true);
+  }
+  return Group(global_group);
+}
+
+namespace detail {
+
+Stream communication_stream() {
+  static Stream comm_stream = new_stream(Device::cpu);
+  return comm_stream;
+}
+
+void all_sum(Group group_, const array& input_, array& output) {
+  auto group = std::static_pointer_cast<GroupImpl>(group_.raw_group());
+  array input = ensure_row_contiguous(input_);
+
+  int size = group->size();
+  int rank = group->rank();
+
+  if ((size & (size - 1)) != 0) {
+    throw std::runtime_error("Only powers of 2 are currently supported");
+  }
+
+  // If not inplace all reduce then copy the input to the output first.
+  if (input.data<void>() != output.data<void>()) {
+    std::memcpy(output.data<char>(), input.data<char>(), input.nbytes());
+  }
+
+  // Butterfly all reduce
+  for (int distance = 1; distance <= size / 2; distance *= 2) {
+    group->send_recv_sum(output, rank ^ distance);
+  }
+}
+
+void all_gather(Group group_, const array& input_, array& output) {
+  auto group = std::static_pointer_cast<GroupImpl>(group_.raw_group());
+  array input = ensure_row_contiguous(input_);
+  std::future<void> sent;
+  std::future<void> received;
+
+  int rank = group->rank();
+  int size = group->size();
+
+  if ((size & (size - 1)) != 0) {
+    throw std::runtime_error("Only powers of 2 are currently supported");
+  }
+
+  // Butterfly all gather
+  int peer = rank ^ 1;
+  if (peer < rank) {
+    received = group->recv_async(
+        output.data<char>() + peer * input.nbytes(), input.nbytes(), peer);
+    sent = group->send_async(input.data<char>(), input.nbytes(), peer);
+  } else {
+    sent = group->send_async(input.data<char>(), input.nbytes(), peer);
+    received = group->recv_async(
+        output.data<char>() + peer * input.nbytes(), input.nbytes(), peer);
+  }
+  std::memcpy(
+      output.data<char>() + rank * input.nbytes(),
+      input.data<char>(),
+      input.nbytes());
+
+  for (int distance = 2; distance <= size / 2; distance *= 2) {
+    sent.wait();
+    received.wait();
+    int peer = rank ^ distance;
+    int their_offset = peer & ~(distance - 1);
+    int our_offset = rank & ~(distance - 1);
+
+    if (peer < rank) {
+      received = group->recv_async(
+          output.data<char>() + their_offset * input.nbytes(),
+          distance * input.nbytes(),
+          peer);
+      sent = group->send_async(
+          output.data<char>() + our_offset * input.nbytes(),
+          distance * input.nbytes(),
+          peer);
+    } else {
+      sent = group->send_async(
+          output.data<char>() + our_offset * input.nbytes(),
+          distance * input.nbytes(),
+          peer);
+      received = group->recv_async(
+          output.data<char>() + their_offset * input.nbytes(),
+          distance * input.nbytes(),
+          peer);
+    }
+  }
+  sent.wait();
+  received.wait();
+}
+
+void send(Group group_, const array& input_, int dst) {
+  array input = ensure_row_contiguous(input_);
+  auto group = std::static_pointer_cast<GroupImpl>(group_.raw_group());
+  group->send(input.data<char>(), input.nbytes(), dst);
+}
+
+void recv(Group group_, array& out, int src) {
+  auto group = std::static_pointer_cast<GroupImpl>(group_.raw_group());
+  group->recv(out.data<char>(), out.nbytes(), src);
+}
+
+} // namespace detail
+
+} // namespace mlx::core::distributed

mlx/io/safetensors.cpp

@@ -1,5 +1,5 @@
 // Copyright © 2023 Apple Inc.
-//
+
 #include <json.hpp>
 #include <stack>
 

python/src/distributed.cpp

@@ -44,7 +44,8 @@ void init_distributed(nb::module_& parent_module) {
               color (int): A value to group processes into subgroups.
               key (int, optional): A key to optionally change the rank ordering
                 of the processes.
-          )pbdoc");
+          )pbdoc")
+      .def("barrier", &distributed::Group::barrier, "Make a synhronization point for all nodes in the group");
 
   m.def(
       "is_available",