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feat: scalar paged prefill fallback and decode causal fix

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- Add scalar paged prefill kernel mirroring split-Q MMA indexing for sm<80
- Wire scalar path into dispatch_paged_prefill under ASTRAI_NO_MMA
- Fix paged decode scalar causal mask dropping all kv>0 for decode
This commit is contained in:
ViperEkura
2026-08-01 16:52:01 +08:00
parent fda82ee232
commit 925cbedc93
3 changed files with 142 additions and 4 deletions
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csrc/kernels/attn_dispatchers.cuh
+13
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@@ -8,6 +8,7 @@
#include "attn_prefill_split_q.cuh"
#include "attn_decode_split_kv.cuh"
#include "attn_paged_decode_split_kv.cuh"
#include "attn_paged_prefill_split_q.cuh"
#ifndef ASTRAI_NO_MMA
#include "attn_prefill_split_q_mma.cuh"
#include "attn_decode_split_kv_mma.cuh"
@@ -208,6 +209,16 @@ static inline void launch_paged_prefill_mma(PagedAttentionParams<bf16>& p) {
}
#endif
template <int HEAD_DIM, bool IsCausal, bool HasMask>
static inline void launch_paged_prefill_scalar(PagedAttentionParams<bf16>& p) {
constexpr int G = 8, ROWS = 32, P_BC = 32;
int max_q_tiles = (p.max_q_len + ROWS - 1) / ROWS;
dim3 grid(max_q_tiles, p.q_head, p.batch);
dim3 block(G, ROWS);
paged_attn_prefill_split_q_kernel<HEAD_DIM, G, ROWS, P_BC, IsCausal, HasMask>
<<<grid, block>>>(p);
}
template <int HEAD_DIM>
static inline void dispatch_paged_prefill(PagedAttentionParams<bf16>& p) {
bool is_causal = (p.causal_offset >= 0);
@@ -215,5 +226,7 @@ static inline void dispatch_paged_prefill(PagedAttentionParams<bf16>& p) {
#ifndef ASTRAI_NO_MMA
DISPATCH_CAUSAL_MASK(is_causal, has_mask, launch_paged_prefill_mma, HEAD_DIM, p);
#else
DISPATCH_CAUSAL_MASK(is_causal, has_mask, launch_paged_prefill_scalar, HEAD_DIM, p);
#endif
}