Files
AstrAI/csrc/kernels/attn_prefill.cu
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ViperEkura a01e8bbe98 refactor: adopt FA2-style KernelTraits + compile-time causal/mask dispatch
- Introduce KernelTraits<HEAD_DIM, BC, WARPS, STAGES> compile-time config bundle, replacing scattered <KD, NC8, KT2, ...> template params
- Template all MMA and scalar kernels on IsCausal/HasMask bools to eliminate inner-loop runtime branches
- Dispatch to 4-path IsCausal/HasMask kernel variants at entry points based on p.causal_offset and p.use_mask
- Update standalone test files with new kernel signatures, add causal test cases
- Fix duplicate using bf16 in MMA kernels that include attn_mma_utils.cuh
2026-07-21 21:52:46 +08:00

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#include "attn_prefill_split_q.cuh"
#include "attn_entry_utils.cuh"
#ifndef ASTRAI_NO_MMA
#include "attn_prefill_split_q_mma.cuh"
template <int HEAD_DIM, bool IsCausal, bool HasMask>
static void launch_mma_prefill(AttentionParams<bf16>& p) {
constexpr int WARPS = 4;
constexpr int BC = (HEAD_DIM <= 128) ? 32 : 16;
using Traits = KernelTraits<HEAD_DIM, BC, WARPS, 2>;
dim3 grid((p.q_len + Traits::BR * WARPS - 1) / (Traits::BR * WARPS),
p.q_head, p.batch);
dim3 block(Traits::NUM_THREADS, 1, 1);
attn_prefill_split_q_mma_kernel<Traits, IsCausal, HasMask><<<grid, block>>>(p);
}
#endif
template <int HEAD_DIM, bool IsCausal, bool HasMask>
static void launch_scalar_prefill(AttentionParams<bf16>& p) {
constexpr int G = 8, ROWS = 32, P_BC = 32;
dim3 grid((p.q_len + ROWS - 1) / ROWS, p.q_head, p.batch);
dim3 block(G, ROWS, 1);
attn_prefill_split_q_kernel_t<HEAD_DIM, G, ROWS, P_BC, IsCausal, HasMask><<<grid, block>>>(p);
}
template <int HEAD_DIM>
static void dispatch_prefill(AttentionParams<bf16>& p) {
bool is_causal = (p.causal_offset >= 0);
bool has_mask = (p.use_mask && p.mask);
#ifndef ASTRAI_NO_MMA
if (is_causal) {
if (has_mask) launch_mma_prefill<HEAD_DIM, true, true>(p);
else launch_mma_prefill<HEAD_DIM, true, false>(p);
} else {
if (has_mask) launch_mma_prefill<HEAD_DIM, false, true>(p);
else launch_mma_prefill<HEAD_DIM, false, false>(p);
}
#else
if (is_causal) {
if (has_mask) launch_scalar_prefill<HEAD_DIM, true, true>(p);
else launch_scalar_prefill<HEAD_DIM, true, false>(p);
} else {
if (has_mask) launch_scalar_prefill<HEAD_DIM, false, true>(p);
else launch_scalar_prefill<HEAD_DIM, false, false>(p);
}
#endif
}
torch::Tensor attn_prefill(
torch::Tensor q,
torch::Tensor k,
torch::Tensor v,
c10::optional<torch::Tensor> mask,
int64_t causal_offset,
double scale,
int64_t layout
) {
AttentionParams<bf16> p;
attn_pack_params(q, k, v, mask, causal_offset, scale, layout, p);
TORCH_CHECK(p.head_dim % 16 == 0, "head_dim must be multiple of 16");
auto O = torch::empty_strided(q.sizes(), q.strides(), q.options());
auto O_view = (layout == 1) ? O.transpose(1, 2) : O;
p.o = (bf16*)O_view.data_ptr();
DISPATCH_HEAD_DIM(p.head_dim, dispatch_prefill, p);
return O;
}
PYBIND11_MODULE(TORCH_EXTENSION_NAME, m) {
m.def("attn_prefill", &attn_prefill,
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") = 0,
"GQA prefill (tensor-core mma on sm_80+, scalar fallback)");
}