Lumpiasty/llama.cpp
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

ggml-webgpu: makes the flash attn vec path subgroup-aware (#23040)

Browse Source 
* ggml-webgpu: makes the flash attn vec path compile and size its split/reduce work from the device’s reported subgroup range instead of assuming 32 subgroup size.

* ggml-webgpu: remove the extra max_wg_size >= max_subgroup_size guard. Remove hardcoded 32 when determine the value of reduce_wg_size and vec_nwg_cap
This commit is contained in:
Zheyuan Chen
2026-05-14 09:31:36 -07:00
committed by GitHub
parent 0c3e4fccca
commit 5ec717d125
2 changed files with 16 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files
ggml/src/ggml-webgpu/ggml-webgpu-shader-lib.hpp
+9 -4
View File
@@ -770,9 +770,14 @@ inline ggml_webgpu_flash_attn_decisions ggml_webgpu_flash_attn_get_decisions(
(v_offset_elems % GGML_WEBGPU_FLASH_ATTN_TILE_KV_VEC_WIDTH == 0u);
const bool kv_vec_type_supported =
K->type == GGML_TYPE_F16 || K->type == GGML_TYPE_Q4_0 || K->type == GGML_TYPE_Q8_0;
const bool use_vec = context.supports_subgroups && (context.src0->ne[1] < 20) && (context.src0->ne[0] % 32 == 0) &&
(context.src2->ne[0] % GGML_WEBGPU_FLASH_ATTN_TILE_KV_VEC_WIDTH == 0) &&
kv_vec_type_supported && (K->type != GGML_TYPE_F16 || f16_vec4_aligned) &&
const uint32_t kv_vec_head_align = K->type == GGML_TYPE_F16 ? GGML_WEBGPU_FLASH_ATTN_TILE_KV_VEC_WIDTH :
(uint32_t) ggml_blck_size(K->type);
const bool kv_vec_head_dims_aligned = context.src0->ne[0] % kv_vec_head_align == 0 &&
context.src2->ne[0] % kv_vec_head_align == 0;
// Compile with enough invocations to cover the largest reported subgroup.
const bool use_vec = context.supports_subgroups && (context.src0->ne[1] < 20) &&
kv_vec_head_dims_aligned && kv_vec_type_supported &&
(K->type != GGML_TYPE_F16 || f16_vec4_aligned) &&
(context.src2->type == K->type);
const bool tile_can_dispatch_all_q_rows =
context.max_subgroup_size > 0 &&
@@ -808,7 +813,7 @@ inline ggml_webgpu_flash_attn_decisions ggml_webgpu_flash_attn_get_decisions(
decisions.q_tile = 1u;
decisions.kv_tile = std::max(8u, std::min(32u, max_kv_tile));
decisions.kv_tile = (decisions.kv_tile / 8u) * 8u;
decisions.wg_size = std::max(1u, std::min<uint32_t>(32u, context.max_subgroup_size));
decisions.wg_size = context.max_subgroup_size;
if (decisions.kv_direct) {
decisions.kv_tile = std::min(decisions.kv_tile, GGML_WEBGPU_KV_SEQ_PAD);
while (GGML_WEBGPU_KV_SEQ_PAD % decisions.kv_tile != 0) {