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Fix unintuitive metal kernel caching (#2242)

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* Fix unintuitive metal kernel caching

* alternative solution
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Awni Hannun 2025-06-06 20:08:15 -07:00 committed by GitHub
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96
docs/src/dev/custom_metal_kernels.rst
View File

@ -8,11 +8,12 @@ MLX supports writing custom Metal kernels through the Python and C++ APIs.
Simple Example
--------------
.. currentmodule:: mlx.core
Let's write a custom kernel that computes ``exp`` elementwise:
.. code-block:: python
def exp_elementwise(a: mx.array):
source = """
uint elem = thread_position_in_grid.x;
T tmp = inp[elem];
@ -25,6 +26,8 @@ Let's write a custom kernel that computes ``exp`` elementwise:
output_names=["out"],
source=source,
)
def exp_elementwise(a: mx.array):
outputs = kernel(
inputs=[a],
template=[("T", mx.float32)],
@ -39,8 +42,13 @@ Let's write a custom kernel that computes ``exp`` elementwise:
b = exp_elementwise(a)
assert mx.allclose(b, mx.exp(a))
Every time you make a kernel, a new Metal library is created and possibly
JIT compiled. To reduce the overhead from that, build the kernel once with
:func:`fast.metal_kernel` and then use it many times.
.. note::
We are only required to pass the body of the Metal kernel in ``source``.
Only pass the body of the Metal kernel in ``source``. The function
signature is generated automatically.
The full function signature will be generated using:
@ -78,29 +86,34 @@ Putting this all together, the generated function signature for ``myexp`` is as
template [[host_name("custom_kernel_myexp_float")]] [[kernel]] decltype(custom_kernel_myexp_float<float>) custom_kernel_myexp_float<float>;
Note: ``grid`` and ``threadgroup`` are parameters to the Metal `dispatchThreads <https://developer.apple.com/documentation/metal/mtlcomputecommandencoder/2866532-dispatchthreads>`_ function.
This means we will launch ``mx.prod(grid)`` threads, subdivided into ``threadgroup`` size threadgroups.
For optimal performance, each thread group dimension should be less than or equal to the corresponding grid dimension.
Note: ``grid`` and ``threadgroup`` are parameters to the Metal `dispatchThreads
<https://developer.apple.com/documentation/metal/mtlcomputecommandencoder/2866532-dispatchthreads>`_
function. This means we will launch ``mx.prod(grid)`` threads, subdivided into
``threadgroup`` size threadgroups. For optimal performance, each thread group
dimension should be less than or equal to the corresponding grid dimension.
Passing ``verbose=True`` to ``mx.fast.metal_kernel.__call__`` will print the generated code for debugging purposes.
Passing ``verbose=True`` to :func:`ast.metal_kernel.__call__` will print the
generated code for debugging purposes.
Using Shape/Strides
-------------------
``mx.fast.metal_kernel`` supports an argument ``ensure_row_contiguous`` which is ``True`` by default.
This will copy the ``mx.array`` inputs if needed before the kernel is launched to ensure that the memory layout is row contiguous.
Generally this makes writing the kernel easier, since we don't have to worry about gaps or the ordering of the dims
when indexing.
:func:`fast.metal_kernel` supports an argument ``ensure_row_contiguous`` which
is ``True`` by default. This will copy the array inputs if needed
before the kernel is launched to ensure that the memory layout is row
contiguous. Generally this makes writing the kernel easier, since we don't
have to worry about gaps or the ordering of the dims when indexing.
If we want to avoid this copy, ``metal_kernel`` automatically passes ``a_shape``, ``a_strides`` and ``a_ndim`` for each
input array ``a`` if any are present in ``source``.
We can then use MLX's built in indexing utils to fetch the right elements for each thread.
If we want to avoid this copy, :func:`fast.metal_kernel` automatically passes
``a_shape``, ``a_strides`` and ``a_ndim`` for each input array ``a`` if any are
present in ``source``. We can then use MLX's built in indexing utils to fetch
the right elements for each thread.
Let's convert ``myexp`` above to support arbitrarily strided arrays without relying on a copy from ``ensure_row_contiguous``:
Let's convert ``myexp`` above to support arbitrarily strided arrays without
relying on a copy from ``ensure_row_contiguous``:
.. code-block:: python
def exp_elementwise(a: mx.array):
source = """
uint elem = thread_position_in_grid.x;
// Utils from `mlx/backend/metal/kernels/utils.h` are automatically included
@ -116,6 +129,8 @@ Let's convert ``myexp`` above to support arbitrarily strided arrays without rely
output_names=["out"],
source=source
)
def exp_elementwise(a: mx.array):
outputs = kernel(
inputs=[a],
template=[("T", mx.float32)],
@ -183,25 +198,13 @@ We'll start with the following MLX implementation using standard ops:
return output
Now let's use ``mx.custom_function`` together with ``mx.fast.metal_kernel``
Now let's use :func:`custom_function` together with :func:`fast.metal_kernel`
to write a fast GPU kernel for both the forward and backward passes.
First we'll implement the forward pass as a fused kernel:
.. code-block:: python
@mx.custom_function
def grid_sample(x, grid):
assert x.ndim == 4, "`x` must be 4D."
assert grid.ndim == 4, "`grid` must be 4D."
B, _, _, C = x.shape
_, gN, gM, D = grid.shape
out_shape = (B, gN, gM, C)
assert D == 2, "Last dim of `grid` must be size 2."
source = """
uint elem = thread_position_in_grid.x;
int H = x_shape[1];
@ -251,12 +254,26 @@ First we'll implement the forward pass as a fused kernel:
out[elem] = nw * I_nw + ne * I_ne + sw * I_sw + se * I_se;
"""
kernel = mx.fast.metal_kernel(
name="grid_sample",
input_names=["x", "grid"],
output_names=["out"],
source=source,
)
@mx.custom_function
def grid_sample(x, grid):
assert x.ndim == 4, "`x` must be 4D."
assert grid.ndim == 4, "`grid` must be 4D."
B, _, _, C = x.shape
_, gN, gM, D = grid.shape
out_shape = (B, gN, gM, C)
assert D == 2, "Last dim of `grid` must be size 2."
outputs = kernel(
inputs=[x, grid],
template=[("T", x.dtype)],
@ -281,11 +298,11 @@ On an M1 Max, we see a big performance improvement:
Grid Sample VJP
---------------
Since we decorated ``grid_sample`` with ``mx.custom_function``, we can now define
its custom vjp transform so MLX can differentiate it.
Since we decorated ``grid_sample`` with :func:`custom_function`, we can now
define its custom vjp transform so MLX can differentiate it.
The backwards pass requires atomically updating ``x_grad``/``grid_grad`` and so
requires a few extra ``mx.fast.metal_kernel`` features:
requires a few extra :func:`fast.metal_kernel` features:
* ``init_value=0``
Initialize all of the kernel's outputs to this value before it runs. This allows us to update only part of the output arrays with the kernel.
@ -299,14 +316,6 @@ We can then implement the backwards pass as follows:
.. code-block:: python
@grid_sample.vjp
def grid_sample_vjp(primals, cotangent, _):
x, grid = primals
B, _, _, C = x.shape
_, gN, gM, D = grid.shape
assert D == 2, "Last dim of `grid` must be size 2."
source = """
uint elem = thread_position_in_grid.x;
int H = x_shape[1];
@ -406,6 +415,15 @@ We can then implement the backwards pass as follows:
source=source,
atomic_outputs=True,
)
@grid_sample.vjp
def grid_sample_vjp(primals, cotangent, _):
x, grid = primals
B, _, _, C = x.shape
_, gN, gM, D = grid.shape
assert D == 2, "Last dim of `grid` must be size 2."
# pad the output channels to simd group size
# so that our `simd_sum`s don't overlap.
simdgroup_size = 32

6
docs/src/dev/extensions.rst
View File

@ -397,11 +397,11 @@ below.
std::ostringstream kname;
kname << "axpby_" << "general_" << type_to_name(out);
// Make sure the metal library is available
d.register_library("mlx_ext");
// Load the metal library
auto lib = d.get_library("mlx_ext");
// Make a kernel from this metal library
auto kernel = d.get_kernel(kname.str(), "mlx_ext");
auto kernel = d.get_kernel(kname.str(), lib);
// Prepare to encode kernel
auto& compute_encoder = d.get_command_encoder(s.index);

6
examples/extensions/axpby/axpby.cpp
View File

@ -172,11 +172,11 @@ void Axpby::eval_gpu(
kname << (contiguous_kernel ? "contiguous_" : "general_");
kname << type_to_name(out);
// Make sure the metal library is available
d.register_library("mlx_ext");
// Load the metal library
auto lib = d.get_library("mlx_ext");
// Make a kernel from this metal library
auto kernel = d.get_kernel(kname.str(), "mlx_ext");
auto kernel = d.get_kernel(kname.str(), lib);
// Prepare to encode kernel
auto& compute_encoder = d.get_command_encoder(s.index);

2
mlx/backend/metal/conv.cpp
View File

@ -677,7 +677,7 @@ void depthwise_conv_2D_gpu(
std::string hash_name = kname.str();
auto& compute_encoder = d.get_command_encoder(s.index);
auto kernel = d.get_kernel(base_name, "mlx", hash_name, func_consts);
auto kernel = d.get_kernel(base_name, hash_name, func_consts);
compute_encoder.set_compute_pipeline_state(kernel);
compute_encoder.set_input_array(in, 0);

344
mlx/backend/metal/custom_kernel.cpp
View File

@ -1,12 +1,326 @@
// Copyright © 2024 Apple Inc.
#include <iostream>
#include <regex>
#include "mlx/backend/common/compiled.h"
#include "mlx/backend/gpu/copy.h"
#include "mlx/backend/metal/jit/includes.h"
#include "mlx/backend/metal/utils.h"
#include "mlx/fast.h"
#include "mlx/fast_primitives.h"
#include "mlx/utils.h"
namespace mlx::core::fast {
struct CustomKernelCache {
std::unordered_map<std::string, std::string> libraries;
};
static CustomKernelCache& cache() {
static CustomKernelCache cache_;
return cache_;
};
std::string write_signature(
std::string func_name,
const std::string& header,
const std::string& source,
const std::vector<std::string>& input_names,
const std::vector<array>& inputs,
const std::vector<std::string>& output_names,
const std::vector<Dtype>& output_dtypes,
const std::vector<std::pair<std::string, TemplateArg>>& template_args,
const std::vector<std::string>& attributes,
const std::vector<CustomKernelShapeInfo>& shape_infos,
bool atomic_outputs) {
std::string kernel_source;
kernel_source.reserve(header.size() + source.size() + 16384);
kernel_source += header;
// Auto-generate a function signature based on `template_args`
// and the dtype/shape of the arrays passed as `inputs`.
if (!template_args.empty()) {
kernel_source += "template <";
int i = 0;
for (const auto& [name, arg] : template_args) {
std::string param_type;
if (std::holds_alternative<int>(arg)) {
param_type = "int";
} else if (std::holds_alternative<bool>(arg)) {
param_type = "bool";
} else if (std::holds_alternative<Dtype>(arg)) {
param_type = "typename";
}
if (i > 0) {
kernel_source += ", ";
}
kernel_source += param_type;
kernel_source += " ";
kernel_source += name;
i++;
}
kernel_source += ">\n";
}
kernel_source += "[[kernel]] void ";
kernel_source += func_name;
kernel_source += "(\n";
int index = 0;
constexpr int max_constant_array_size = 8;
// Add inputs
for (int i = 0; i < inputs.size(); ++i) {
const auto& name = input_names[i];
const auto& arr = inputs[i];
auto dtype = get_type_string(arr.dtype());
std::string location =
arr.size() < max_constant_array_size ? "constant" : "device";
std::string ref = arr.ndim() == 0 ? "&" : "*";
kernel_source += " const ";
kernel_source += location;
kernel_source += " ";
kernel_source += dtype;
kernel_source += ref;
kernel_source += " ";
kernel_source += name;
kernel_source += " [[buffer(";
kernel_source += std::to_string(index);
kernel_source += ")]],\n";
index++;
// Add input shape, strides and ndim if present in the source
if (arr.ndim() > 0) {
if (shape_infos[i].shape) {
kernel_source +=
(" const constant int* " + name + "_shape [[buffer(" +
std::to_string(index) + ")]],\n");
index++;
}
if (shape_infos[i].strides) {
kernel_source +=
(" const constant int64_t* " + name + "_strides [[buffer(" +
std::to_string(index) + ")]],\n");
index++;
}
if (shape_infos[i].ndim) {
kernel_source +=
(" const constant int& " + name + "_ndim [[buffer(" +
std::to_string(index) + ")]],\n");
index++;
}
}
}
// Add outputs
for (int i = 0; i < output_names.size(); ++i) {
const auto& name = output_names[i];
const auto& dtype = output_dtypes[i];
kernel_source += " device ";
auto type_string = get_type_string(dtype);
if (atomic_outputs) {
kernel_source += "atomic<";
}
kernel_source += type_string;
if (atomic_outputs) {
kernel_source += ">";
}
kernel_source += "* ";
kernel_source += name;
kernel_source += " [[buffer(";
kernel_source += std::to_string(index);
kernel_source += ")]]";
if (index < inputs.size() + output_names.size() - 1 ||
attributes.size() > 0) {
kernel_source += ",\n";
} else {
kernel_source += ") {\n";
}
index++;
}
index = 0;
for (const auto& attr : attributes) {
kernel_source += attr;
if (index < attributes.size() - 1) {
kernel_source += ",\n";
} else {
kernel_source += ") {\n";
}
index++;
}
kernel_source += source;
kernel_source += "\n}\n";
return kernel_source;
}
std::string write_template(
const std::vector<std::pair<std::string, TemplateArg>>& template_args) {
std::ostringstream template_def;
template_def << "<";
int i = 0;
for (const auto& [name, arg] : template_args) {
if (i > 0) {
template_def << ", ";
}
if (std::holds_alternative<int>(arg)) {
template_def << std::get<int>(arg);
} else if (std::holds_alternative<bool>(arg)) {
template_def << std::get<bool>(arg);
} else if (std::holds_alternative<Dtype>(arg)) {
template_def << get_type_string(std::get<Dtype>(arg));
}
i++;
}
template_def << ">";
return template_def.str();
}
MetalKernelFunction metal_kernel(
const std::string& name,
const std::vector<std::string>& input_names,
const std::vector<std::string>& output_names,
const std::string& source,
const std::string& header /* = "" */,
bool ensure_row_contiguous /* = true */,
bool atomic_outputs /* = false */) {
if (output_names.empty()) {
throw std::invalid_argument(
"[metal_kernel] Must specify at least one output.");
}
std::vector<CustomKernelShapeInfo> shape_infos;
for (auto& n : input_names) {
CustomKernelShapeInfo shape_info;
shape_info.shape = source.find(n + "_shape") != std::string::npos;
shape_info.strides = source.find(n + "_strides") != std::string::npos;
shape_info.ndim = source.find(n + "_ndim") != std::string::npos;
shape_infos.push_back(shape_info);
}
const std::vector<std::pair<std::string, std::string>> metal_attributes = {
{"dispatch_quadgroups_per_threadgroup", "uint"},
{"dispatch_simdgroups_per_threadgroup", "uint"},
{"dispatch_threads_per_threadgroup", "uint3"},
{"grid_origin", "uint3"},
{"grid_size", "uint3"},
{"quadgroup_index_in_threadgroup", "uint"},
{"quadgroups_per_threadgroup", "uint"},
{"simdgroup_index_in_threadgroup", "uint"},
{"simdgroups_per_threadgroup", "uint"},
{"thread_execution_width", "uint"},
{"thread_index_in_quadgroup", "uint"},
{"thread_index_in_simdgroup", "uint"},
{"thread_index_in_threadgroup", "uint"},
{"thread_position_in_grid", "uint3"},
{"thread_position_in_threadgroup", "uint3"},
{"threadgroup_position_in_grid", "uint3"},
{"threadgroups_per_grid", "uint3"},
{"threads_per_grid", "uint3"},
{"threads_per_simdgroup", "uint"},
{"threads_per_threadgroup", "uint3"},
};
std::vector<std::string> attributes;
for (const auto& [attr, dtype] : metal_attributes) {
if (source.find(attr) != std::string::npos) {
attributes.push_back(" " + dtype + " " + attr + " [[" + attr + "]]");
}
}
return [=,
shape_infos = std::move(shape_infos),
attributes = std::move(attributes)](
const std::vector<array>& inputs,
const std::vector<Shape>& output_shapes,
const std::vector<Dtype>& output_dtypes,
std::tuple<int, int, int> grid,
std::tuple<int, int, int> threadgroup,
const std::vector<std::pair<std::string, TemplateArg>>&
template_args = {},
std::optional<float> init_value = std::nullopt,
bool verbose = false,
StreamOrDevice s_ = {}) {
if (inputs.size() != input_names.size()) {
std::ostringstream msg;
msg << "[metal_kernel] Expected `inputs` to have size "
<< input_names.size() << " but got size " << inputs.size() << "."
<< std::endl;
throw std::invalid_argument(msg.str());
}
if (output_shapes.size() != output_names.size()) {
std::ostringstream msg;
msg << "[metal_kernel] Expected `output_shapes` to have size "
<< output_names.size() << " but got size " << output_shapes.size()
<< "." << std::endl;
throw std::invalid_argument(msg.str());
}
if (output_dtypes.size() != output_names.size()) {
std::ostringstream msg;
msg << "[metal_kernel] Expected `output_dtypes` to have size "
<< output_names.size() << " but got size " << output_dtypes.size()
<< "." << std::endl;
throw std::invalid_argument(msg.str());
}
auto s = to_stream(s_);
if (s.device != Device::gpu) {
throw std::invalid_argument("[metal_kernel] Only supports the GPU.");
}
std::string kernel_name = "custom_kernel_" + name;
std::string template_def = "";
if (!template_args.empty()) {
std::regex disallowed_chars("\\<|\\>|(, )");
template_def = write_template(template_args);
auto template_hash =
std::regex_replace(template_def, disallowed_chars, "_");
template_hash.pop_back();
kernel_name += "_";
kernel_name += template_hash;
}
std::string kernel_source = write_signature(
kernel_name,
header,
source,
input_names,
inputs,
output_names,
output_dtypes,
template_args,
attributes,
shape_infos,
atomic_outputs);
if (!template_args.empty()) {
template_def = kernel_name + template_def;
kernel_source += "\ntemplate [[host_name(\"";
kernel_source += kernel_name;
kernel_source += "\")]] [[kernel]] decltype(";
kernel_source += template_def;
kernel_source += ") ";
kernel_source += template_def;
kernel_source += ";\n";
}
if (verbose) {
std::cout << "Generated source code for `" << name << "`:" << std::endl
<< "```" << std::endl
<< kernel_source << std::endl
<< "```" << std::endl;
}
return array::make_arrays(
std::move(output_shapes),
std::move(output_dtypes),
std::make_shared<CustomKernel>(
s,
std::move(kernel_name),
std::move(kernel_source),
grid,
threadgroup,
shape_infos,
ensure_row_contiguous,
init_value),
std::move(inputs));
};
}
void CustomKernel::eval_gpu(
const std::vector<array>& inputs,
std::vector<array>& outputs) {
@ -39,9 +353,23 @@ void CustomKernel::eval_gpu(
}
auto& d = metal::device(s.device);
const auto& lib_name = name_;
auto lib =
d.get_library(lib_name, [this] { return metal::utils() + source_; });
{
// Clear kernels from the device library cache if needed
auto& kernel_cache = cache();
if (auto it = kernel_cache.libraries.find(name_);
it != kernel_cache.libraries.end()) {
if (it->second != source_) {
auto& d = metal::device(s.device);
d.clear_library(name_);
it->second = source_;
}
} else {
kernel_cache.libraries.emplace(name_, source_);
}
}
auto lib = d.get_library(name_, [this] { return metal::utils() + source_; });
auto kernel = d.get_kernel(name_, lib);
auto& compute_encoder = d.get_command_encoder(s.index);
compute_encoder.set_compute_pipeline_state(kernel);
@ -73,6 +401,16 @@ void CustomKernel::eval_gpu(
}
const auto [tx, ty, tz] = threadgroup_;
auto tg_size = tx * ty * tz;
auto max_tg_size = kernel->maxTotalThreadsPerThreadgroup();
if (tg_size > max_tg_size) {
std::ostringstream msg;
msg << "Thread group size (" << tg_size << ") is greater than "
<< " the maximum allowed threads per threadgroup (" << max_tg_size
<< ").";
throw std::invalid_argument(msg.str());
}
const auto [gx, gy, gz] = grid_;
MTL::Size group_dims =
MTL::Size(std::min(tx, gx), std::min(ty, gy), std::min(tz, gz));

64
mlx/backend/metal/device.cpp
View File

@ -295,7 +295,7 @@ void CommandEncoder::barrier() {
Device::Device() {
auto pool = new_scoped_memory_pool();
device_ = load_device();
library_map_ = {{"mlx", load_default_library(device_)}};
default_library_ = load_default_library(device_);
arch_ = std::string(device_->architecture()->name()->utf8String());
auto arch = arch_.back();
switch (arch) {
@ -326,11 +326,11 @@ Device::Device() {
Device::~Device() {
auto pool = new_scoped_memory_pool();
for (auto& k : kernel_map_) {
k.second->release();
for (auto& [l, kernel_map] : library_kernels_) {
l->release();
for (auto& [_, k] : kernel_map) {
k->release();
}
for (auto& l : library_map_) {
l.second->release();
}
stream_map_.clear();
device_->release();
@ -474,13 +474,24 @@ CommandEncoder& Device::get_command_encoder(int index) {
return *stream.encoder;
}
void Device::register_library(
const std::string& lib_name,
const std::string& lib_path) {
if (auto it = library_map_.find(lib_name); it == library_map_.end()) {
auto new_lib = load_library(device_, lib_name, lib_path.c_str());
library_map_.insert({lib_name, new_lib});
MTL::Library* Device::get_library(
const std::string& name,
const std::string& path /* = "" */) {
{
std::shared_lock rlock(library_mtx_);
if (auto it = library_map_.find(name); it != library_map_.end()) {
return it->second;
}
}
std::unique_lock wlock(library_mtx_);
if (auto it = library_map_.find(name); it != library_map_.end()) {
return it->second;
}
auto new_lib = load_library(device_, name, path.c_str());
library_map_.insert({name, new_lib});
return new_lib;
}
MTL::Library* Device::build_library_(const std::string& source_string) {
@ -649,6 +660,19 @@ MTL::Library* Device::get_library(
return mtl_lib;
}
void Device::clear_library(const std::string& name) {
std::unique_lock wlock(library_mtx_);
if (auto it = library_map_.find(name); it != library_map_.end()) {
auto kernel_map_it = library_kernels_.find(it->second);
for (auto& [_, kernel] : kernel_map_it->second) {
kernel->release();
}
library_kernels_.erase(kernel_map_it);
it->second->release();
library_map_.erase(it);
}
}
MTL::LinkedFunctions* Device::get_linked_functions_(
const std::vector<MTL::Function*>& funcs) {
if (funcs.empty()) {
@ -679,6 +703,7 @@ MTL::ComputePipelineState* Device::get_kernel_(
std::unique_lock wlock(kernel_mtx_);
// Try loading again to avoid loading twice
auto& kernel_map_ = library_kernels_[mtl_lib];
if (auto it = kernel_map_.find(hash_name); it != kernel_map_.end()) {
return it->second;
}
@ -713,6 +738,7 @@ MTL::ComputePipelineState* Device::get_kernel(
std::shared_lock lock(kernel_mtx_);
// Look for cached kernel
auto& kernel_map_ = library_kernels_[mtl_lib];
if (auto it = kernel_map_.find(kname); it != kernel_map_.end()) {
return it->second;
}
@ -722,23 +748,11 @@ MTL::ComputePipelineState* Device::get_kernel(
MTL::ComputePipelineState* Device::get_kernel(
const std::string& base_name,
const std::string& lib_name /* = "mlx" */,
const std::string& hash_name /* = "" */,
const MTLFCList& func_consts /* = {} */,
const std::vector<MTL::Function*>& linked_functions /* = {} */) {
const auto& kname = hash_name.size() == 0 ? base_name : hash_name;
{
// Multiple readers allowed
std::shared_lock lock(kernel_mtx_);
// Look for cached kernel
if (auto it = kernel_map_.find(kname); it != kernel_map_.end()) {
return it->second;
}
}
// Search for cached metal lib
MTL::Library* mtl_lib = get_library_(lib_name);
return get_kernel_(base_name, mtl_lib, kname, func_consts, linked_functions);
return get_kernel(
base_name, default_library_, hash_name, func_consts, linked_functions);
}
void Device::set_residency_set(const MTL::ResidencySet* residency_set) {

16
mlx/backend/metal/device.h
View File

@ -187,14 +187,16 @@ class Device {
CommandEncoder& get_command_encoder(int index);
void end_encoding(int index);
void register_library(
const std::string& lib_name,
const std::string& lib_path = "");
MTL::Library* get_library(
const std::string& name,
const std::string& path = "");
MTL::Library* get_library(
const std::string& name,
const std::function<std::string(void)>& builder);
void clear_library(const std::string& name);
MTL::ComputePipelineState* get_kernel(
const std::string& base_name,
MTL::Library* mtl_lib,
@ -204,7 +206,6 @@ class Device {
MTL::ComputePipelineState* get_kernel(
const std::string& base_name,
const std::string& lib_name = "mlx",
const std::string& hash_name = "",
const MTLFCList& func_consts = {},
const std::vector<MTL::Function*>& linked_functions = {});
@ -258,10 +259,13 @@ class Device {
std::unordered_map<int32_t, DeviceStream> stream_map_;
std::shared_mutex kernel_mtx_;
std::unordered_map<std::string, MTL::ComputePipelineState*> kernel_map_;
std::shared_mutex library_mtx_;
std::unordered_map<std::string, MTL::Library*> library_map_;
MTL::Library* default_library_;
std::unordered_map<
MTL::Library*,
std::unordered_map<std::string, MTL::ComputePipelineState*>>
library_kernels_;
const MTL::ResidencySet* residency_set_{nullptr};
std::string arch_;
int max_ops_per_buffer_;

8
mlx/backend/metal/nojit_kernels.cpp
View File

@ -146,7 +146,7 @@ MTL::ComputePipelineState* get_steel_gemm_fused_kernel(
int,
int,
int) {
return d.get_kernel(kernel_name, "mlx", hash_name, func_consts);
return d.get_kernel(kernel_name, hash_name, func_consts);
}
MTL::ComputePipelineState* get_steel_gemm_splitk_kernel(
@ -207,7 +207,7 @@ MTL::ComputePipelineState* get_steel_gemm_gather_kernel(
int,
int,
bool) {
return d.get_kernel(kernel_name, "mlx", hash_name, func_consts);
return d.get_kernel(kernel_name, hash_name, func_consts);
}
MTL::ComputePipelineState* get_gemv_masked_kernel(
@ -259,7 +259,7 @@ MTL::ComputePipelineState* get_fft_kernel(
const std::string& hash_name,
const metal::MTLFCList& func_consts,
const std::string&) {
return d.get_kernel(kernel_name, "mlx", hash_name, func_consts);
return d.get_kernel(kernel_name, hash_name, func_consts);
}
MTL::ComputePipelineState* get_quantized_kernel(
@ -283,7 +283,7 @@ MTL::ComputePipelineState* get_gather_qmm_kernel(
int,
int,
bool) {
return d.get_kernel(kernel_name, "mlx", hash_name, func_consts);
return d.get_kernel(kernel_name, hash_name, func_consts);
}
} // namespace mlx::core

4
mlx/backend/metal/normalization.cpp
View File

@ -172,7 +172,7 @@ void RMSNormVJP::eval_gpu(
auto& compute_encoder = d.get_command_encoder(s.index);
{
auto kernel = d.get_kernel(op_name, "mlx", hash_name, func_consts);
auto kernel = d.get_kernel(op_name, hash_name, func_consts);
MTL::Size grid_dims, group_dims;
if (axis_size <= looped_limit) {
@ -395,7 +395,7 @@ void LayerNormVJP::eval_gpu(
};
{
auto kernel = d.get_kernel(op_name, "mlx", hash_name, func_consts);
auto kernel = d.get_kernel(op_name, hash_name, func_consts);
MTL::Size grid_dims, group_dims;
if (axis_size <= looped_limit) {

6
mlx/backend/metal/scaled_dot_product_attention.cpp
View File

@ -73,7 +73,7 @@ void sdpa_full_self_attention_metal(
std::string hash_name = kname.str();
auto& compute_encoder = d.get_command_encoder(s.index);
auto kernel = d.get_kernel(base_name, "mlx", hash_name, func_consts);
auto kernel = d.get_kernel(base_name, hash_name, func_consts);
compute_encoder.set_compute_pipeline_state(kernel);
const int NQ = (qL + bq - 1) / bq;
@ -180,7 +180,7 @@ void sdpa_vector(
// Get the kernel
auto& compute_encoder = d.get_command_encoder(s.index);
auto kernel = d.get_kernel(kname, "mlx", hash_name, func_consts);
auto kernel = d.get_kernel(kname, hash_name, func_consts);
compute_encoder.set_compute_pipeline_state(kernel);
// Set its arguments
@ -281,7 +281,7 @@ void sdpa_vector_2pass(
// Get the kernel
auto& compute_encoder = d.get_command_encoder(s.index);
auto kernel = d.get_kernel(kname, "mlx", hash_name, func_consts);
auto kernel = d.get_kernel(kname, hash_name, func_consts);
compute_encoder.set_compute_pipeline_state(kernel);

13
mlx/backend/no_gpu/primitives.cpp
View File

@ -2,6 +2,7 @@
#include "mlx/primitives.h"
#include "mlx/distributed/primitives.h"
#include "mlx/fast.h"
#include "mlx/fast_primitives.h"
#define NO_GPU_MULTI(func) \
@ -155,6 +156,18 @@ NO_GPU_USE_FALLBACK(RoPE)
NO_GPU(ScaledDotProductAttention)
NO_GPU_MULTI(AffineQuantize)
NO_GPU_MULTI(CustomKernel)
MetalKernelFunction metal_kernel(
const std::string&,
const std::vector<std::string>&,
const std::vector<std::string>&,
const std::string&,
const std::string&,
bool ensure_row_contiguous,
bool atomic_outputs) {
throw std::runtime_error("[metal_kernel] No GPU back-end.");
}
} // namespace fast
namespace distributed {

302
mlx/fast.cpp
View File

@ -1,10 +1,7 @@
// Copyright © 2023-2024 Apple Inc.
#include <cassert>
#include <iostream>
#include <numeric>
#include <regex>
#include "mlx/backend/common/compiled.h"
#include "mlx/fast.h"
#include "mlx/fast_primitives.h"
#include "mlx/ops.h"
@ -1027,303 +1024,4 @@ std::vector<Shape> AffineQuantize::output_shapes(
}
}
std::string write_signature(
std::string func_name,
const std::string& header,
const std::string& source,
const std::vector<std::string>& input_names,
const std::vector<array>& inputs,
const std::vector<std::string>& output_names,
const std::vector<Dtype>& output_dtypes,
const std::vector<std::pair<std::string, TemplateArg>>& template_args,
const std::vector<std::string>& attributes,
const std::vector<CustomKernelShapeInfo>& shape_infos,
bool atomic_outputs) {
std::string kernel_source;
kernel_source.reserve(header.size() + source.size() + 16384);
kernel_source += header;
// Auto-generate a function signature based on `template_args`
// and the dtype/shape of the arrays passed as `inputs`.
if (!template_args.empty()) {
kernel_source += "template <";
int i = 0;
for (const auto& [name, arg] : template_args) {
std::string param_type;
if (std::holds_alternative<int>(arg)) {
param_type = "int";
} else if (std::holds_alternative<bool>(arg)) {
param_type = "bool";
} else if (std::holds_alternative<Dtype>(arg)) {
param_type = "typename";
}
if (i > 0) {
kernel_source += ", ";
}
kernel_source += param_type;
kernel_source += " ";
kernel_source += name;
i++;
}
kernel_source += ">\n";
}
kernel_source += "[[kernel]] void ";
kernel_source += func_name;
kernel_source += "(\n";
int index = 0;
constexpr int max_constant_array_size = 8;
// Add inputs
for (int i = 0; i < inputs.size(); ++i) {
const auto& name = input_names[i];
const auto& arr = inputs[i];
auto dtype = get_type_string(arr.dtype());
std::string location =
arr.size() < max_constant_array_size ? "constant" : "device";
std::string ref = arr.ndim() == 0 ? "&" : "*";
kernel_source += " const ";
kernel_source += location;
kernel_source += " ";
kernel_source += dtype;
kernel_source += ref;
kernel_source += " ";
kernel_source += name;
kernel_source += " [[buffer(";
kernel_source += std::to_string(index);
kernel_source += ")]],\n";
index++;
// Add input shape, strides and ndim if present in the source
if (arr.ndim() > 0) {
if (shape_infos[i].shape) {
kernel_source +=
(" const constant int* " + name + "_shape [[buffer(" +
std::to_string(index) + ")]],\n");
index++;
}
if (shape_infos[i].strides) {
kernel_source +=
(" const constant int64_t* " + name + "_strides [[buffer(" +
std::to_string(index) + ")]],\n");
index++;
}
if (shape_infos[i].ndim) {
kernel_source +=
(" const constant int& " + name + "_ndim [[buffer(" +
std::to_string(index) + ")]],\n");
index++;
}
}
}
// Add outputs
for (int i = 0; i < output_names.size(); ++i) {
const auto& name = output_names[i];
const auto& dtype = output_dtypes[i];
kernel_source += " device ";
auto type_string = get_type_string(dtype);
if (atomic_outputs) {
kernel_source += "atomic<";
}
kernel_source += type_string;
if (atomic_outputs) {
kernel_source += ">";
}
kernel_source += "* ";
kernel_source += name;
kernel_source += " [[buffer(";
kernel_source += std::to_string(index);
kernel_source += ")]]";
if (index < inputs.size() + output_names.size() - 1 ||
attributes.size() > 0) {
kernel_source += ",\n";
} else {
kernel_source += ") {\n";
}
index++;
}
index = 0;
for (const auto& attr : attributes) {
kernel_source += attr;
if (index < attributes.size() - 1) {
kernel_source += ",\n";
} else {
kernel_source += ") {\n";
}
index++;
}
kernel_source += source;
kernel_source += "\n}\n";
return kernel_source;
}
std::string write_template(
const std::vector<std::pair<std::string, TemplateArg>>& template_args) {
std::ostringstream template_def;
template_def << "<";
int i = 0;
for (const auto& [name, arg] : template_args) {
if (i > 0) {
template_def << ", ";
}
if (std::holds_alternative<int>(arg)) {
template_def << std::get<int>(arg);
} else if (std::holds_alternative<bool>(arg)) {
template_def << std::get<bool>(arg);
} else if (std::holds_alternative<Dtype>(arg)) {
template_def << get_type_string(std::get<Dtype>(arg));
}
i++;
}
template_def << ">";
return template_def.str();
}
MetalKernelFunction metal_kernel(
const std::string& name,
const std::vector<std::string>& input_names,
const std::vector<std::string>& output_names,
const std::string& source,
const std::string& header /* = "" */,
bool ensure_row_contiguous /* = true */,
bool atomic_outputs /* = false */) {
if (output_names.empty()) {
throw std::invalid_argument(
"[metal_kernel] Must specify at least one output.");
}
std::vector<CustomKernelShapeInfo> shape_infos;
for (auto& n : input_names) {
CustomKernelShapeInfo shape_info;
shape_info.shape = source.find(n + "_shape") != std::string::npos;
shape_info.strides = source.find(n + "_strides") != std::string::npos;
shape_info.ndim = source.find(n + "_ndim") != std::string::npos;
shape_infos.push_back(shape_info);
}
const std::vector<std::pair<std::string, std::string>> metal_attributes = {
{"dispatch_quadgroups_per_threadgroup", "uint"},
{"dispatch_simdgroups_per_threadgroup", "uint"},
{"dispatch_threads_per_threadgroup", "uint3"},
{"grid_origin", "uint3"},
{"grid_size", "uint3"},
{"quadgroup_index_in_threadgroup", "uint"},
{"quadgroups_per_threadgroup", "uint"},
{"simdgroup_index_in_threadgroup", "uint"},
{"simdgroups_per_threadgroup", "uint"},
{"thread_execution_width", "uint"},
{"thread_index_in_quadgroup", "uint"},
{"thread_index_in_simdgroup", "uint"},
{"thread_index_in_threadgroup", "uint"},
{"thread_position_in_grid", "uint3"},
{"thread_position_in_threadgroup", "uint3"},
{"threadgroup_position_in_grid", "uint3"},
{"threadgroups_per_grid", "uint3"},
{"threads_per_grid", "uint3"},
{"threads_per_simdgroup", "uint"},
{"threads_per_threadgroup", "uint3"},
};
std::vector<std::string> attributes;
for (const auto& [attr, dtype] : metal_attributes) {
if (source.find(attr) != std::string::npos) {
attributes.push_back(" " + dtype + " " + attr + " [[" + attr + "]]");
}
}
return [=,
shape_infos = std::move(shape_infos),
attributes = std::move(attributes)](
const std::vector<array>& inputs,
const std::vector<Shape>& output_shapes,
const std::vector<Dtype>& output_dtypes,
std::tuple<int, int, int> grid,
std::tuple<int, int, int> threadgroup,
const std::vector<std::pair<std::string, TemplateArg>>&
template_args = {},
std::optional<float> init_value = std::nullopt,
bool verbose = false,
StreamOrDevice s_ = {}) {
if (inputs.size() != input_names.size()) {
std::ostringstream msg;
msg << "[metal_kernel] Expected `inputs` to have size "
<< input_names.size() << " but got size " << inputs.size() << "."
<< std::endl;
throw std::invalid_argument(msg.str());
}
if (output_shapes.size() != output_names.size()) {
std::ostringstream msg;
msg << "[metal_kernel] Expected `output_shapes` to have size "
<< output_names.size() << " but got size " << output_shapes.size()
<< "." << std::endl;
throw std::invalid_argument(msg.str());
}
if (output_dtypes.size() != output_names.size()) {
std::ostringstream msg;
msg << "[metal_kernel] Expected `output_dtypes` to have size "
<< output_names.size() << " but got size " << output_dtypes.size()
<< "." << std::endl;
throw std::invalid_argument(msg.str());
}
auto s = to_stream(s_);
if (s.device != Device::gpu) {
throw std::invalid_argument("[metal_kernel] Only supports the GPU.");
}
std::ostringstream func_name;
std::string template_def = "";
std::string hash_key = "";
if (!template_args.empty()) {
std::regex disallowed_chars("\\<|\\>|(, )");
template_def = write_template(template_args);
hash_key = std::regex_replace(template_def, disallowed_chars, "_");
hash_key.pop_back();
}
func_name << "custom_kernel_" << name << hash_key;
std::string kernel_name = func_name.str();
std::string kernel_source = write_signature(
kernel_name,
header,
source,
input_names,
inputs,
output_names,
output_dtypes,
template_args,
attributes,
shape_infos,
atomic_outputs);
if (!template_args.empty()) {
template_def = kernel_name + template_def;
kernel_source += "\ntemplate [[host_name(\"";
kernel_source += kernel_name;
kernel_source += "\")]] [[kernel]] decltype(";
kernel_source += template_def;
kernel_source += ") ";
kernel_source += template_def;
kernel_source += ";\n";
}
if (verbose) {
std::cout << "Generated source code for `" << name << "`:" << std::endl
<< "```" << std::endl
<< kernel_source << std::endl
<< "```" << std::endl;
}
return array::make_arrays(
std::move(output_shapes),
std::move(output_dtypes),
std::make_shared<CustomKernel>(
s,
std::move(kernel_name),
std::move(kernel_source),
grid,
threadgroup,
shape_infos,
ensure_row_contiguous,
init_value),
std::move(inputs));
};
}
} // namespace mlx::core::fast

35
python/tests/test_fast.py
View File

@ -735,6 +735,41 @@ class TestFast(mlx_tests.MLXTestCase):
)[0]
self.assertEqual(out.item(), 2)
@unittest.skipIf(not mx.metal.is_available(), "Metal is not available")
def test_custom_kernel_caching(self):
def call_kernel(a: mx.array, source):
kernel = mx.fast.metal_kernel(
name="my_kernel",
input_names=["inp"],
output_names=["out"],
source=source,
)
return kernel(
inputs=[a],
grid=(a.size, 1, 1),
threadgroup=(a.size, 1, 1),
output_shapes=[a.shape],
output_dtypes=[a.dtype],
stream=mx.gpu,
)[0]
a = mx.random.normal(shape=(32,))
source = """
uint elem = thread_position_in_grid.x;
out[elem] = 0.0;
"""
out = call_kernel(a, source)
self.assertTrue(mx.array_equal(out, mx.zeros_like(out)))
source = """
uint elem = thread_position_in_grid.x;
out[elem] = 1.0;
"""
out = call_kernel(a, source)
self.assertTrue(mx.array_equal(out, mx.ones_like(out)))
if __name__ == "__main__":
unittest.main()