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ggml : add support for non-padded FA KV #16148

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ggml : add support for non-padded FA KV #16148

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defeeb3
metal : pad K, V and Mask when needed
ggerganov Sep 21, 2025
5ed8acd
cont : simplify
ggerganov Sep 28, 2025
ea8f4bb
cuda : add TODO about KV padding requirement
ggerganov Sep 28, 2025
9b21358
metal : add comments
ggerganov Sep 28, 2025
347c113
metal : remove mask padding requirement
ggerganov Sep 28, 2025
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6 changes: 6 additions & 0 deletions ggml/src/ggml-cuda/fattn.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -208,6 +208,12 @@ static best_fattn_kernel ggml_cuda_get_best_fattn_kernel(const int device, const

const int cc = ggml_cuda_info().devices[device].cc;

// TODO: temporary until support is extended
// https://github.com/ggml-org/llama.cpp/pull/16148#issuecomment-3343525206
if (K->ne[1] % FATTN_KQ_STRIDE != 0) {
return BEST_FATTN_KERNEL_NONE;
}

switch (K->ne[0]) {
case 64:
case 128:
Expand Down
60 changes: 58 additions & 2 deletions ggml/src/ggml-metal/ggml-metal-device.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -918,13 +918,58 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_argsort(ggml_metal_library
return res;
}

ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_pad(
ggml_metal_library_t lib,
const struct ggml_tensor * op,
bool has_mask,
int32_t ncpsg) {
assert(op->op == GGML_OP_FLASH_ATTN_EXT);
GGML_UNUSED(op);

char base[256];
char name[256];

snprintf(base, 256, "kernel_%s",
"flash_attn_ext_pad");

snprintf(name, 256, "%s_mask=%d_ncpsg=%d",
base,
has_mask,
ncpsg);

ggml_metal_pipeline_t res = ggml_metal_library_get_pipeline(lib, name);
if (res) {
return res;
}

ggml_metal_cv_t cv = ggml_metal_cv_init();

ggml_metal_cv_set_bool(cv, has_mask, FC_FLASH_ATTN_EXT_PAD + 0);
//ggml_metal_cv_set_bool(cv, has_sinks, FC_FLASH_ATTN_EXT_PAD + 1);
//ggml_metal_cv_set_bool(cv, has_bias, FC_FLASH_ATTN_EXT_PAD + 2);
//ggml_metal_cv_set_bool(cv, has_scap, FC_FLASH_ATTN_EXT_PAD + 3);

//ggml_metal_cv_set_int32(cv, ns10, FC_FLASH_ATTN_EXT_PAD + 20);
//ggml_metal_cv_set_int32(cv, ns20, FC_FLASH_ATTN_EXT_PAD + 21);
//ggml_metal_cv_set_int32(cv, nsg, FC_FLASH_ATTN_EXT_PAD + 22);
//ggml_metal_cv_set_int32(cv, nwg, FC_FLASH_ATTN_EXT_PAD + 23);
ggml_metal_cv_set_int32(cv, ncpsg, FC_FLASH_ATTN_EXT_PAD + 24);

res = ggml_metal_library_compile_pipeline(lib, base, name, cv);

ggml_metal_cv_free(cv);

return res;
}

ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext(
ggml_metal_library_t lib,
const ggml_tensor * op,
bool has_mask,
bool has_sinks,
bool has_bias,
bool has_scap,
bool has_kvpad,
int32_t nsg) {
assert(op->op == GGML_OP_FLASH_ATTN_EXT);

Expand All @@ -937,18 +982,23 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext(
const int32_t ns10 = op->src[1]->nb[1]/op->src[1]->nb[0];
const int32_t ns20 = op->src[2]->nb[1]/op->src[2]->nb[0];

// do bounds checks for the mask?
const bool bc_mask = op->src[3] && (op->src[3]->ne[1] % 8 != 0);

snprintf(base, 256, "kernel_%s_%s_dk%d_dv%d",
"flash_attn_ext",
ggml_type_name(op->src[1]->type),
dk,
dv);

snprintf(name, 256, "%s_mask=%d_sinks=%d_bias=%d_scap=%d_ns10=%d_ns20=%d_nsg=%d",
snprintf(name, 256, "%s_mask=%d_sinks=%d_bias=%d_scap=%d_kvpad=%d_bcm=%d_ns10=%d_ns20=%d_nsg=%d",
base,
has_mask,
has_sinks,
has_bias,
has_scap,
has_kvpad,
bc_mask,
ns10,
ns20,
nsg);
Expand All @@ -964,6 +1014,9 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext(
ggml_metal_cv_set_bool(cv, has_sinks, FC_FLASH_ATTN_EXT + 1);
ggml_metal_cv_set_bool(cv, has_bias, FC_FLASH_ATTN_EXT + 2);
ggml_metal_cv_set_bool(cv, has_scap, FC_FLASH_ATTN_EXT + 3);
ggml_metal_cv_set_bool(cv, has_kvpad, FC_FLASH_ATTN_EXT + 4);

ggml_metal_cv_set_bool(cv, bc_mask, FC_FLASH_ATTN_EXT + 10);

ggml_metal_cv_set_int32(cv, ns10, FC_FLASH_ATTN_EXT + 20);
ggml_metal_cv_set_int32(cv, ns20, FC_FLASH_ATTN_EXT + 21);
Expand All @@ -983,6 +1036,7 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_vec(
bool has_sinks,
bool has_bias,
bool has_scap,
bool has_kvpad,
int32_t nsg,
int32_t nwg) {
assert(op->op == GGML_OP_FLASH_ATTN_EXT);
Expand All @@ -1002,12 +1056,13 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_vec(
dk,
dv);

snprintf(name, 256, "%s_mask=%d_sink=%d_bias=%d_softcap=%d_ns10=%d_ns20=%d_nsg=%d_nwg=%d",
snprintf(name, 256, "%s_mask=%d_sink=%d_bias=%d_scap=%d_kvpad=%d_ns10=%d_ns20=%d_nsg=%d_nwg=%d",
base,
has_mask,
has_sinks,
has_bias,
has_scap,
has_kvpad,
ns10,
ns20,
nsg, nwg);
Expand All @@ -1023,6 +1078,7 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_vec(
ggml_metal_cv_set_bool(cv, has_sinks, FC_FLASH_ATTN_EXT_VEC + 1);
ggml_metal_cv_set_bool(cv, has_bias, FC_FLASH_ATTN_EXT_VEC + 2);
ggml_metal_cv_set_bool(cv, has_scap, FC_FLASH_ATTN_EXT_VEC + 3);
ggml_metal_cv_set_bool(cv, has_kvpad, FC_FLASH_ATTN_EXT_VEC + 4);

ggml_metal_cv_set_int32(cv, ns10, FC_FLASH_ATTN_EXT_VEC + 20);
ggml_metal_cv_set_int32(cv, ns20, FC_FLASH_ATTN_EXT_VEC + 21);
Expand Down
8 changes: 8 additions & 0 deletions ggml/src/ggml-metal/ggml-metal-device.h
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Original file line number Diff line number Diff line change
Expand Up @@ -135,13 +135,20 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_pad_reflect_1d (ggml_me
ggml_metal_pipeline_t ggml_metal_library_get_pipeline_arange (ggml_metal_library_t lib, const struct ggml_tensor * op);
ggml_metal_pipeline_t ggml_metal_library_get_pipeline_timestep_embedding(ggml_metal_library_t lib, const struct ggml_tensor * op);

ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_pad(
ggml_metal_library_t lib,
const struct ggml_tensor * op,
bool has_mask,
int32_t ncpsg);

ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext(
ggml_metal_library_t lib,
const struct ggml_tensor * op,
bool has_mask,
bool has_sinks,
bool has_bias,
bool has_scap,
bool has_kvpad,
int32_t nsg);

ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_vec(
Expand All @@ -151,6 +158,7 @@ ggml_metal_pipeline_t ggml_metal_library_get_pipeline_flash_attn_ext_vec(
bool has_sinks,
bool has_bias,
bool has_scap,
bool has_kvpad,
int32_t nsg,
int32_t nwg);

Expand Down
31 changes: 26 additions & 5 deletions ggml/src/ggml-metal/ggml-metal-impl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -69,11 +69,12 @@
#define N_SG_IQ4_XS 2

// function constants offsets
#define FC_FLASH_ATTN_EXT 100
#define FC_FLASH_ATTN_EXT_VEC 200
#define FC_FLASH_ATTN_EXT_VEC_REDUCE 300
#define FC_MUL_MV 400
#define FC_MUL_MM 500
#define FC_FLASH_ATTN_EXT_PAD 100
#define FC_FLASH_ATTN_EXT 200
#define FC_FLASH_ATTN_EXT_VEC 300
#define FC_FLASH_ATTN_EXT_VEC_REDUCE 400
#define FC_MUL_MV 500
#define FC_MUL_MM 600

// kernel argument structs
//
Expand Down Expand Up @@ -243,6 +244,24 @@ typedef struct {
int32_t sect_3;
} ggml_metal_kargs_rope;

typedef struct {
int32_t ne11;
int32_t ne_12_2; // assume K and V are same shape
int32_t ne_12_3;
uint64_t nb11;
uint64_t nb12;
uint64_t nb13;
uint64_t nb21;
uint64_t nb22;
uint64_t nb23;
int32_t ne31;
int32_t ne32;
int32_t ne33;
uint64_t nb31;
uint64_t nb32;
uint64_t nb33;
} ggml_metal_kargs_flash_attn_ext_pad;

typedef struct {
int32_t ne01;
int32_t ne02;
Expand All @@ -261,6 +280,7 @@ typedef struct {
uint64_t nb21;
uint64_t nb22;
uint64_t nb23;
int32_t ne31;
int32_t ne32;
int32_t ne33;
uint64_t nb31;
Expand Down Expand Up @@ -295,6 +315,7 @@ typedef struct {
uint64_t nb21;
uint64_t nb22;
uint64_t nb23;
int32_t ne31;
int32_t ne32;
int32_t ne33;
uint64_t nb31;
Expand Down
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