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[CUDA] Faster general copy #2873

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Merged
awni merged 1 commit into from
Dec 5, 2025
Merged

[CUDA] Faster general copy #2873

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16 changes: 12 additions & 4 deletions mlx/backend/cuda/copy/copy_general_input.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand All @@ -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>;
}
Expand All @@ -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(
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2 changes: 0 additions & 2 deletions mlx/backend/gpu/copy.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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());
}
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