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AstrAI/csrc/kernels/attn_decode.cu
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ViperEkura 3439e3104e perf: launch CUDA kernels on torch's current stream
- Thread a cudaStream_t through attn dispatchers onto torch's current stream
- Scope the device guard to the entry function so kernels run on tensor device
- DISPATCH_HEAD_DIM now forwards varargs so stream reaches each dispatch
- Parallelize CPU reference kernels with OpenMP (paged test 31s -> 7s)
- Merge decode/prefill standalone tests into attn_test.cu with correctness tables
- Drop bench error column (CPU ref too slow at large sizes)
- Update cuda_kernels.md for the merged test layout
2026-08-02 13:20:14 +08:00

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#include "attn_dispatchers.cuh"
#include "attn_entry_utils.cuh"
torch::Tensor attn_decode(
torch::Tensor q,
torch::Tensor k,
torch::Tensor v,
c10::optional<torch::Tensor> mask,
int64_t causal_offset,
double scale,
int64_t layout
) {
const at::cuda::OptionalCUDAGuard device_guard(device_of(q));
auto stream = at::cuda::getCurrentCUDAStream();
AttentionParams<bf16> p;
attn_pack_params(q, k, v, mask, causal_offset, scale, layout, p);
TORCH_CHECK(p.q_len == 1, "Q seq_len must be 1");
TORCH_CHECK(p.head_dim % 32 == 0, "head_dim must be multiple of 32");
auto O = torch::empty_strided(q.sizes(), q.strides(), q.options());
auto O_view = (layout == BLHD) ? O.transpose(1, 2) : O;
p.o = (bf16*)O_view.data_ptr();
alloc_split_partials(p);
DISPATCH_HEAD_DIM(p.head_dim, dispatch_decode, p, stream);
C10_CUDA_CHECK(cudaGetLastError());
return O;
}
PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
m.def("attn_decode", &attn_decode,
py::arg("q"),
py::arg("k"),
py::arg("v"),
py::arg("mask") = py::none(),
py::arg("causal_offset") = -1,
py::arg("scale") = 0.0,
py::arg("layout") = (int64_t)BHLD,
"GQA decode (tensor-core head-packing on sm_80+, scalar fallback)");
}