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Vulkan Flash Attention Coopmat1 Refactor (#19075)

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* vulkan: use coopmat for flash attention p*v matrix multiplication

* fix P loading issue

* fix barrier position

* remove reduction that is no longer needed

* move max thread reduction into loop

* remove osh padding

* add bounds checks and padding

* remove unused code

* fix shmem sizes, loop duration and accesses

* don't overwrite Qf, add new shared psh buffer instead

* add missing bounds checks

* use subgroup reductions

* optimize

* move bounds check, reduce barriers

* support other Bc values and other subgroup sizes

* remove D_split

* replace Of register array with shared memory Ofsh array

* parallelize HSV across the rowgroups

* go back to Of in registers, not shmem

* vectorize sfsh

* don't store entire K tile in shmem

* fixes

* load large k tiles to shmem on Nvidia

* adapt shared memory host check function to shader changes

* remove Bc 32 case

* remove unused variable

* fix missing mask reduction tmspsh barrier

* fix mask bounds check

* fix rowmax f16 under/overflow to inf

* fix flash_attn_cm2 BLOCK_SIZE preprocessor directives
This commit is contained in:
Ruben Ortlam
2026-01-28 18:52:45 +01:00
committed by GitHub
parent 72d3b1898a
commit f6b533d898
4 changed files with 329 additions and 185 deletions
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ggml/src/ggml-vulkan/ggml-vulkan.cpp
+43 -21
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@@ -3162,17 +3162,31 @@ static void ggml_vk_load_shaders(vk_device& device) {
// For scalar, use 128 (arbitrary)
// The same D_split value is used for both HSK and HSV, so just base it on the union of the LSBs.
const uint32_t D = (hsk|hsv);
uint32_t wg_size = (path == FA_SCALAR || path == FA_COOPMAT1)
? scalar_flash_attention_workgroup_size
: ((small_rows && (D % 32) == 0) ? 256 : 128);
auto rows_cols = fa_rows_cols(path, hsk, hsv, clamp, type, small_rows, small_cache);
uint32_t wg_size;
switch (path) {
case FA_COOPMAT2:
wg_size = ((small_rows && (D % 32) == 0) ? 256 : 128);
break;
case FA_COOPMAT1:
wg_size = (rows_cols[1] / 16) * device->subgroup_size; // enough subgroups for Bc/MatBc
break;
default:
wg_size = scalar_flash_attention_workgroup_size;
break;
}
// D_split can't be larger than a subgroup because we use subgroupShuffle to reduce it.
// D_split can't be larger than the LSB of D divided by 4 due to vectorization in the shader.
const uint32_t D_lsb = D ^ (D & (D-1));
uint32_t D_split = std::min(std::min(device->subgroup_size, 8u), D_lsb / 4);
return {wg_size, rows_cols[0], rows_cols[1], hsk, hsv, clamp, D_split};
// Nvidia prefers shared memory use to load large tiles of K
// AMD prefers loading K directly from global memory
const uint32_t k_load_shmem = device->vendor_id == VK_VENDOR_ID_NVIDIA ? 1 : 0;
return {wg_size, rows_cols[0], rows_cols[1], hsk, hsv, clamp, D_split, device->subgroup_size, k_load_shmem};
};
#define CREATE_FA(TYPE, NAMELC, FAPATH, SUFFIX) \
@@ -3187,15 +3201,15 @@ static void ggml_vk_load_shaders(vk_device& device) {
if (path == FAPATH) { \
if (aligned) { \
if (f32acc) { \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f32acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? 32 : 0)); \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f32acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0)); \
} else { \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f16acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? 32 : 0)); \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_aligned_f16acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,0,TYPE,small_rows,small_cache), fa_align(FAPATH,HSK,HSV,TYPE,small_rows,small_cache), true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0)); \
} \
} else { \
if (f32acc) { \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f32acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), 1, true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? 32 : 0)); \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f32acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), 1, true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0)); \
} else { \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f16acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), 1, true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? 32 : 0)); \
ggml_vk_create_pipeline(device, fa.second, "flash_attn_f32_f16_f16acc" #NAMELC, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _len, flash_attn_f32_f16_ ## NAMELC ## _f16acc ## SUFFIX ## _data, "main", 6, sizeof(vk_flash_attn_push_constants), fa_wg_denoms(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), fa_spec_constants(FAPATH, HSK,HSV,1,TYPE,small_rows,small_cache), 1, true, FAPATH==FA_COOPMAT1, (FAPATH==FA_COOPMAT1 ? device->subgroup_size : 0)); \
} \
} \
} \
@@ -8344,41 +8358,49 @@ static bool ggml_vk_flash_attn_scalar_shmem_support(const vk_device& device, con
const uint32_t total_size = tmpsh + tmpshv4 + masksh + Qf;
const bool supported = total_size <= device->properties.limits.maxComputeSharedMemorySize;
VK_LOG_DEBUG("ggml_vk_flash_attn_coopmat_shmem_support(HSK=" << hsk << ", HSV=" << hsv << ", total_size=" << total_size << ", supported=" << supported);
VK_LOG_DEBUG("ggml_vk_flash_attn_scalar_shmem_support(HSK=" << hsk << ", HSV=" << hsv << ", total_size=" << total_size << ", supported=" << supported);
return supported;
}
static bool ggml_vk_flash_attn_coopmat_shmem_support(const vk_device& device, const uint32_t hsk, uint32_t hsv, bool f32acc) {
static bool ggml_vk_flash_attn_coopmat_shmem_support(const vk_device& device, const uint32_t hsk, uint32_t hsv, bool f32acc, ggml_type kv_type) {
// Needs to be kept up to date on shader changes
GGML_UNUSED(hsv);
const uint32_t wg_size = scalar_flash_attention_workgroup_size;
const uint32_t Br = coopmat1_flash_attention_num_large_rows;
const uint32_t Bc = scalar_flash_attention_Bc;
const auto rows_cols = fa_rows_cols(FA_COOPMAT1, hsk, hsv, 0, kv_type, false, false);
const uint32_t Br = rows_cols[0];
const uint32_t Bc = rows_cols[1];
const uint32_t MatBr = 16, MatBc = 16;
const uint32_t row_split = Bc / MatBc;
const uint32_t hsk_pad = ROUNDUP_POW2(hsk, 16);
const uint32_t acctype = f32acc ? 4 : 2;
const uint32_t f16vec4 = 8;
const uint32_t tmpsh = wg_size * sizeof(float);
const uint32_t tmpshv4 = wg_size * 4 * acctype;
const uint32_t tmpsh = (Bc / MatBc) * sizeof(float);
const uint32_t qstride = hsk_pad / 4 + 2;
const uint32_t Qf = Br * qstride * f16vec4;
const uint32_t psh_stride = Br / 4 + 2;
const uint32_t Psh = Bc * psh_stride * f16vec4;
const uint32_t sfshstride = (hsk <= 128) ? (Br + 8) : Br;
const uint32_t sfsh = Bc * sfshstride * acctype;
const uint32_t kshstride = hsk_pad / 4 + 2;
const uint32_t ksh = Bc * kshstride * f16vec4;
const bool k_load_shmem = device->vendor_id == VK_VENDOR_ID_NVIDIA;
const uint32_t kshstride = (k_load_shmem ? hsk_pad : MatBr) / 4 + 2;
const uint32_t vsh_stride = MatBc / 4 * row_split;
const uint32_t ksh = ((kshstride >= vsh_stride) ? (Bc * kshstride) : (Bc * vsh_stride)) * f16vec4;
const uint32_t slope = Br * sizeof(float);
const uint32_t slope = Br * acctype;
const uint32_t total_size = tmpsh + tmpshv4 + Qf + sfsh + ksh + slope;
const uint32_t total_size = tmpsh + Qf + Psh + sfsh + ksh + slope;
const bool supported = total_size <= device->properties.limits.maxComputeSharedMemorySize;
VK_LOG_DEBUG("ggml_vk_flash_attn_coopmat_shmem_support(HSK=" << hsk << ", HSV=" << hsv << ", f32acc=" << f32acc << ", total_size=" << total_size << ", supported=" << supported);
VK_LOG_DEBUG("ggml_vk_flash_attn_coopmat_shmem_support(HSK=" << hsk << ", HSV=" << hsv << ", f32acc=" << f32acc << ", kv_type=" << kv_type << ", total_size=" << total_size << ", supported=" << supported);
return supported;
}
@@ -8442,7 +8464,7 @@ static void ggml_vk_flash_attn(ggml_backend_vk_context * ctx, vk_context& subctx
const bool coopmat_shape_supported = (dst->op_params[3] == GGML_PREC_F32 && ctx->device->coopmat_support_16x16x16_f32acc) ||
(dst->op_params[3] != GGML_PREC_F32 && ctx->device->coopmat_support_16x16x16_f16acc);
const bool coopmat_shmem_supported = ggml_vk_flash_attn_coopmat_shmem_support(ctx->device, HSK, HSV, dst->op_params[3] == GGML_PREC_F32);
const bool coopmat_shmem_supported = ggml_vk_flash_attn_coopmat_shmem_support(ctx->device, HSK, HSV, dst->op_params[3] == GGML_PREC_F32, k->type);
if (!coopmat_shape_supported || !coopmat_shmem_supported) {
path = FA_SCALAR;