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mlx/mlx/backend/cuda/fence.cpp
Awni Hannun df58b4133a
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[CUDA] Reduce use of managed memory (#2725)
* Use async cuda malloc managed with cuda 13

* add pool threshold

* refactor for regular cuda malloc

* load eval gpu for cuda

* remove use of cuda pool, use cuda free async

* fix

* fix

* fix

* fix

* fix + comment
2025-11-05 16:05:23 -08:00

48 lines
1.3 KiB
C++

// Copyright © 2025 Apple Inc.
#include "mlx/fence.h"
#include "mlx/backend/cuda/allocator.h"
#include "mlx/backend/cuda/device.h"
#include "mlx/backend/cuda/event.h"
namespace mlx::core {
struct FenceImpl {
uint32_t count;
cu::AtomicEvent event;
};
Fence::Fence(Stream s) {
fence_ = std::shared_ptr<void>(
new FenceImpl{0}, [](void* ptr) { delete static_cast<FenceImpl*>(ptr); });
}
void Fence::wait(Stream s, const array&) {
auto* fence = static_cast<FenceImpl*>(fence_.get());
fence->event.wait(fence->count);
}
void Fence::update(Stream s, const array& a, bool cross_device) {
auto* fence = static_cast<FenceImpl*>(fence_.get());
if (cross_device) {
// Move to managed memory if there is a device switch
auto& cbuf =
*static_cast<cu::CudaBuffer*>(const_cast<array&>(a).buffer().ptr());
if (cbuf.device != -1) {
void* new_data;
CHECK_CUDA_ERROR(cudaMallocManaged(&new_data, cbuf.size));
cbuf.device = -1;
auto& encoder = cu::device(s.device).get_command_encoder(s);
encoder.commit();
CHECK_CUDA_ERROR(cudaMemcpyAsync(
new_data, cbuf.data, cbuf.size, cudaMemcpyDefault, encoder.stream()));
CHECK_CUDA_ERROR(cudaFreeAsync(cbuf.data, encoder.stream()));
cbuf.data = new_data;
}
}
fence->count++;
fence->event.signal(s, fence->count);
}
} // namespace mlx::core