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refactor: stride-based attn interface with layout and causal mask

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- Replace is_causal + causal_offset with unified causal_offset (-1 = off, >=0 = first Q pos)
- Causal and mask can now coexist (was mutually exclusive)
- Add stride-based addressing for Q/KV/O (layout-agnostic, zero-copy)
- Add layout param ("bhld"/"blhd") parsed in Python, passed as int to C++
- Support 2D [batch, kv_len] and 3D [batch, q_len, kv_len] mask
- Vectorize paged KV gather in Python fallback (was per-token Python loop)
- Extract shared helpers: compute_num_splits, alloc_split_partials, dispatch_head_dim
- Unify paged_decode entry via attn_pack_paged_params
- Update mma_softmax_tile for 3D mask with per-row qrow indexing
This commit is contained in:
ViperEkura
2026-07-14 21:34:42 +08:00
parent 2c7a71a9c0
commit 57729fd92d
18 changed files with 558 additions and 283 deletions
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csrc/tests/test_utils.cuh
+29 -2
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@@ -101,6 +101,32 @@ void dispatch_by_head_dim(int head_dim, Fn&& fn) {
_HeadSwitch<32, 64, 128, 256>::call(head_dim, fn);
}
// Set default strides for contiguous b h l d layout on AttentionParams.
template<typename P>
inline void set_default_strides(P& p) {
p.q_stride_b = p.q_head * p.q_len * p.head_dim;
p.q_stride_h = p.q_len * p.head_dim;
p.q_stride_l = p.head_dim;
p.q_stride_d = 1;
p.kv_stride_b = p.kv_head * p.kv_len * p.head_dim;
p.kv_stride_h = p.kv_len * p.head_dim;
p.kv_stride_l = p.head_dim;
p.kv_stride_d = 1;
p.mask_b_stride = p.kv_len;
p.mask_q_stride = 0;
}
// Set default Q strides for contiguous b h l d layout on PagedAttentionParams.
template<typename P>
inline void set_default_paged_strides(P& p) {
p.q_stride_b = p.q_head * p.q_len * p.head_dim;
p.q_stride_h = p.q_len * p.head_dim;
p.q_stride_l = p.head_dim;
p.q_stride_d = 1;
p.mask_b_stride = p.kv_len;
p.mask_q_stride = 0;
}
// Generic CPU reference for multi-query / grouped-query attention.
// Tensor shapes (all float*):
// Q : [B, Hq, q_len, D]
@@ -108,10 +134,11 @@ void dispatch_by_head_dim(int head_dim, Fn&& fn) {
// V : [B, Hk, kv_len, D]
// O : [B, Hq, q_len, D]
// mask: if q_len == 1, shape is [B, kv_len]; otherwise mask is not supported.
// causal_offset: -1 = non-causal; >=0 = absolute position of first Q token.
static void cpu_attention_ref(
const float* Q, const float* K, const float* V, const bool* mask,
float* O, int B, int Hq, int Hk, int q_len, int kv_len, int D,
int is_causal, int causal_offset
int causal_offset
) {
float scale = 1.0f / sqrtf((float)D);
int n_rep = Hq / Hk;
@@ -122,7 +149,7 @@ static void cpu_attention_ref(
float mv = -INFINITY, sv = 0.0f;
float accum[256] = {0.0f};
int lim = kv_len;
if (is_causal) {
if (causal_offset >= 0) {
int c = qi + causal_offset + 1;
lim = (c < kv_len) ? c : kv_len;
}