From bcb43163aed6a8986cf3d66e90848c9c258d4936 Mon Sep 17 00:00:00 2001 From: Aman Gupta Date: Sun, 25 Jan 2026 23:25:58 +0800 Subject: [PATCH] ggml-cpu: Use tiled FA for prompt-processing (#19012) * ggml-cpu: Use tiled FA for prompt-processing the FA performance is gimped on CPU on long contexts because it essentially uses a vector kernel. This PR adds a tiled FA for PP. Perf tuning for tile sizes done on a AMD EPYC single-socket 64-c machine. * fix out of bounds for mask * skip rows where there are all masks * skip tile if mask is inf * store mask in worksize * check inf tile earlier --- ggml/src/ggml-cpu/common.h | 8 + ggml/src/ggml-cpu/ggml-cpu.c | 9 +- ggml/src/ggml-cpu/ops.cpp | 290 ++++++++++++++++++++++++++++++++++- 3 files changed, 303 insertions(+), 4 deletions(-) diff --git a/ggml/src/ggml-cpu/common.h b/ggml/src/ggml-cpu/common.h index 6adca5437f..1057b5bb15 100644 --- a/ggml/src/ggml-cpu/common.h +++ b/ggml/src/ggml-cpu/common.h @@ -6,6 +6,9 @@ #include "ggml-impl.h" #include "simd-mappings.h" +#define GGML_FA_TILE_Q 32 +#define GGML_FA_TILE_KV 16 + #ifdef __cplusplus #include @@ -84,4 +87,9 @@ static std::pair get_thread_range(const struct ggml_compute_pa return {ir0, ir1}; } +struct ggml_fa_tile_config { + static constexpr size_t Q = GGML_FA_TILE_Q; + static constexpr size_t KV = GGML_FA_TILE_KV; +}; + #endif diff --git a/ggml/src/ggml-cpu/ggml-cpu.c b/ggml/src/ggml-cpu/ggml-cpu.c index 4c7a75e768..b1de2ae871 100644 --- a/ggml/src/ggml-cpu/ggml-cpu.c +++ b/ggml/src/ggml-cpu/ggml-cpu.c @@ -14,6 +14,7 @@ #include "vec.h" #include "ops.h" #include "ggml.h" +#include "common.h" #if defined(_MSC_VER) || defined(__MINGW32__) #include // using malloc.h with MSC/MINGW @@ -2866,10 +2867,12 @@ struct ggml_cplan ggml_graph_plan( } break; case GGML_OP_FLASH_ATTN_EXT: { - const int64_t ne10 = node->src[1]->ne[0]; // DK - const int64_t ne20 = node->src[2]->ne[0]; // DV + const int64_t DK = node->src[1]->ne[0]; + const int64_t DV = node->src[2]->ne[0]; - cur = sizeof(float)*(1*ne10 + 2*ne20)*n_tasks; // 1x head size K + 2x head size V (per thread) + // Tiled flash attention scratch (tile sizes defined in common.h) + // Per-thread: Q_q + KQ + mask + VKQ32 + V32 + padding + cur = sizeof(float)*(GGML_FA_TILE_Q*DK + 2*GGML_FA_TILE_Q*GGML_FA_TILE_KV + GGML_FA_TILE_Q*DV + GGML_FA_TILE_KV*DV)*n_tasks; } break; case GGML_OP_FLASH_ATTN_BACK: { diff --git a/ggml/src/ggml-cpu/ops.cpp b/ggml/src/ggml-cpu/ops.cpp index 387e2fe42c..48c8964361 100644 --- a/ggml/src/ggml-cpu/ops.cpp +++ b/ggml/src/ggml-cpu/ops.cpp @@ -8164,6 +8164,7 @@ static void ggml_compute_forward_flash_attn_ext_f16_one_chunk( // online softmax / attention // loop over n_kv and n_head_kv // ref: https://arxiv.org/pdf/2112.05682.pdf + for (int64_t ic = 0; ic < nek1; ++ic) { const float mv = mp ? slope*GGML_CPU_FP16_TO_FP32(mp[ic]) : 0.0f; if (mv == -INFINITY) { @@ -8271,6 +8272,280 @@ static void ggml_compute_forward_flash_attn_ext_f16_one_chunk( } } +static void ggml_compute_forward_flash_attn_ext_tiled( + const ggml_compute_params * params, + ggml_tensor * dst, + int ir0, int ir1) { + const ggml_tensor * q = dst->src[0]; + const ggml_tensor * k = dst->src[1]; + const ggml_tensor * v = dst->src[2]; + const ggml_tensor * mask = dst->src[3]; + const ggml_tensor * sinks = dst->src[4]; + + GGML_TENSOR_LOCALS(int64_t, neq, q, ne) + GGML_TENSOR_LOCALS(size_t, nbq, q, nb) + GGML_TENSOR_LOCALS(int64_t, nek, k, ne) + GGML_TENSOR_LOCALS(size_t, nbk, k, nb) + GGML_TENSOR_LOCALS(int64_t, nev, v, ne) + GGML_TENSOR_LOCALS(size_t, nbv, v, nb) + GGML_TENSOR_LOCALS(int64_t, ne, dst, ne) + GGML_TENSOR_LOCALS(size_t, nb, dst, nb) + + const int64_t DK = nek0; + const int64_t DV = nev0; + const int64_t N = neq1; + + GGML_ASSERT(ne0 == DV); + GGML_ASSERT(ne2 == N); + + // input tensor rows must be contiguous + GGML_ASSERT(nbq0 == ggml_type_size(q->type)); + GGML_ASSERT(nbk0 == ggml_type_size(k->type)); + GGML_ASSERT(nbv0 == ggml_type_size(v->type)); + + GGML_ASSERT(neq0 == DK); + GGML_ASSERT(nek0 == DK); + GGML_ASSERT(nev0 == DV); + + GGML_ASSERT(neq1 == N); + + // dst cannot be transposed or permuted + GGML_ASSERT(nb0 == sizeof(float)); + GGML_ASSERT(nb0 <= nb1); + GGML_ASSERT(nb1 <= nb2); + GGML_ASSERT(nb2 <= nb3); + + GGML_ASSERT(k->type == v->type); + const ggml_type kv_type = k->type; + + const auto * kv_type_traits_cpu = ggml_get_type_traits_cpu(kv_type); + const ggml_from_float_t kv_from_float = kv_type_traits_cpu->from_float; + const ggml_vec_dot_t kv_vec_dot = kv_type_traits_cpu->vec_dot; + const size_t kv_type_size = ggml_type_size(kv_type); + + // broadcast factors + const int64_t rk2 = neq2/nek2; + const int64_t rk3 = neq3/nek3; + + const int64_t rv2 = neq2/nev2; + const int64_t rv3 = neq3/nev3; + + float scale = 1.0f; + float max_bias = 0.0f; + float logit_softcap = 0.0f; + + memcpy(&scale, (float *) dst->op_params + 0, sizeof(float)); + memcpy(&max_bias, (float *) dst->op_params + 1, sizeof(float)); + memcpy(&logit_softcap, (float *) dst->op_params + 2, sizeof(float)); + + if (logit_softcap != 0) { + scale /= logit_softcap; + } + + const uint32_t n_head = neq2; + const uint32_t n_head_log2 = 1u << (uint32_t) floor(log2(n_head)); + + const float m0 = powf(2.0f, -(max_bias ) / n_head_log2); + const float m1 = powf(2.0f, -(max_bias / 2.0f) / n_head_log2); + + int ith = params->ith; + + static constexpr int Q_TILE_SZ = ggml_fa_tile_config::Q; + static constexpr int KV_TILE_SZ = ggml_fa_tile_config::KV; + + GGML_ASSERT(nek1 % KV_TILE_SZ == 0 && "KV sequence length must be divisible by KV_TILE_SZ"); + + int ir = ir0; + while (ir < ir1) { + // q indices for the start of this tile + const int iq3 = ir/(neq2*neq1); + const int iq2 = (ir - iq3*neq2*neq1)/neq1; + const int iq1 = (ir - iq3*neq2*neq1 - iq2*neq1); + + // Number of valid rows in this tile: + // - limited by tile size (Q_TILE_SZ) + // - limited by chunk boundary (ir1 - ir) + // - limited by head boundary (neq1 - iq1) to avoid crossing into next head + const int tile_rows = MIN(Q_TILE_SZ, MIN((int)(ir1 - ir), (int)(neq1 - iq1))); + GGML_ASSERT(tile_rows > 0); + + const uint32_t h = iq2; // head index + const float slope = (max_bias > 0.0f) ? h < n_head_log2 ? powf(m0, h + 1) : powf(m1, 2*(h - n_head_log2) + 1) : 1.0f; + + float S[Q_TILE_SZ]; + float M[Q_TILE_SZ]; + + for (int i = 0 ; i < Q_TILE_SZ; ++i) { + S[i] = 0.; + M[i] = -INFINITY; + } + + // Per-thread scratch layout: + // Q_q: Q_TILE_SZ * DK (converted Q tile in KV type) + // KQ: Q_TILE_SZ * KV_TILE_SZ (attention scores in float) + // mask: Q_TILE_SZ * KV_TILE_SZ (mask in float) + // VKQ32: Q_TILE_SZ * DV (FP32 output accumulator) + // V32: KV_TILE_SZ * DV (F32 buffer for V tile - used for f166 conversion) + float * base = (float *) params->wdata + ith*(Q_TILE_SZ*DK + 2*Q_TILE_SZ*KV_TILE_SZ + Q_TILE_SZ*DV + KV_TILE_SZ*DV + CACHE_LINE_SIZE_F32); + + void * Q_q = base; + float * KQ = (float *)((char *)base + Q_TILE_SZ * DK * sizeof(float)); + float * mask32 = KQ + Q_TILE_SZ * KV_TILE_SZ; + float * VKQ32 = mask32 + Q_TILE_SZ * KV_TILE_SZ; + float * V32 = VKQ32 + Q_TILE_SZ * DV; // F32 buffer for V tile + + memset(VKQ32, 0, Q_TILE_SZ * DV * sizeof(float)); + memset(mask32, 0, Q_TILE_SZ * KV_TILE_SZ * sizeof(float)); + + // k indices + const int ik3 = iq3 / rk3; + const int ik2 = iq2 / rk2; + + // v indices + const int iv3 = iq3 / rv3; + const int iv2 = iq2 / rv2; + + for (int tq = 0; tq < tile_rows; tq++) { + const float * pq = (const float *) ((char *) q->data + ((iq1 + tq)*nbq1 + iq2*nbq2 + iq3*nbq3)); + kv_from_float(pq, (char *)Q_q + tq * DK * kv_type_size, DK); + } + // Zero-pad remaining rows + for (int tq = tile_rows; tq < Q_TILE_SZ; tq++) { + memset((char *)Q_q + tq * DK * kv_type_size, 0, DK * kv_type_size); + } + + for (int64_t ic = 0; ic < nek1; ic += KV_TILE_SZ) { + + // skip the tile entirely if all the masks are -inf + if (mask) { + bool can_skip = true; + for (int tq = 0; tq < tile_rows; tq++) { + const ggml_fp16_t * mp_row = (const ggml_fp16_t *)((const char *) mask->data + (iq1 + tq)*mask->nb[1] + (iq2%mask->ne[2])*mask->nb[2] + (iq3%mask->ne[3])*mask->nb[3]); + for (int tk = 0; tk < KV_TILE_SZ; tk++) { + mask32[tq * KV_TILE_SZ + tk] = slope * GGML_CPU_FP16_TO_FP32(mp_row[ic + tk]); + if (mask32[tq * KV_TILE_SZ + tk] != -INFINITY) { + can_skip = false; + } + } + } + + if (can_skip) { + continue; + } + } + + for (int tq = 0; tq < Q_TILE_SZ; tq++) { + const void * q_row = (const char *)Q_q + tq * DK * kv_type_size; + for (int tk = 0; tk < KV_TILE_SZ; tk++) { + const void * k_row = (const char *) k->data + ((ic + tk)*nbk1 + ik2*nbk2 + ik3*nbk3); + float s; + kv_vec_dot(DK, &s, 0, k_row, 0, q_row, 0, 1); + KQ[tq * KV_TILE_SZ + tk] = s * scale; + } + } + + if (logit_softcap != 0.0f) { + ggml_vec_tanh_f32(Q_TILE_SZ * KV_TILE_SZ, KQ, KQ); + ggml_vec_scale_f32(Q_TILE_SZ * KV_TILE_SZ, KQ, logit_softcap); + } + + if (mask) { + ggml_vec_add_f32(tile_rows * KV_TILE_SZ, KQ, KQ, mask32); + } + + bool skip[Q_TILE_SZ] = {}; + + for (int tq = 0; tq < Q_TILE_SZ; tq++) { + float * kq_row = KQ + tq * KV_TILE_SZ; + + float tile_max; + ggml_vec_max_f32(KV_TILE_SZ, &tile_max, kq_row); + + if (tile_max == -INFINITY) { + skip[tq] = true; + continue; + } + + const float Mold = M[tq]; + const float Mnew = fmaxf(Mold, tile_max); + + if (Mnew > Mold) { + const float ms = expf(Mold - Mnew); + ggml_vec_scale_f32(DV, VKQ32 + tq * DV, ms); + S[tq] *= ms; + } + M[tq] = Mnew; + + + S[tq] += ggml_vec_soft_max_f32(KV_TILE_SZ, kq_row, kq_row, Mnew); + } + + // Convert V tile to F32 first (if F16), then do MAD + // On x86, ggml_vec_mad_f16 internall converts F16<->F32 on every load/store, so pre-converting is faster. + // TODO: on ARM, native f16 should be faster + if (kv_type == GGML_TYPE_F16) { + for (int tk = 0; tk < KV_TILE_SZ; tk++) { + const ggml_fp16_t * v_row = (const ggml_fp16_t *)((const char *) v->data + ((ic + tk)*nbv1 + iv2*nbv2 + iv3*nbv3)); + ggml_fp16_to_fp32_row(v_row, V32 + tk * DV, DV); + } + for (int tq = 0; tq < Q_TILE_SZ; tq++) { + if (skip[tq]) continue; + float * vkq_row = VKQ32 + tq * DV; + for (int tk = 0; tk < KV_TILE_SZ; tk++) { + const float p = KQ[tq * KV_TILE_SZ + tk]; + ggml_vec_mad_f32(DV, vkq_row, V32 + tk * DV, p); + } + } + } else { + for (int tq = 0; tq < Q_TILE_SZ; tq++) { + if (skip[tq]) continue; + float * vkq_row = VKQ32 + tq * DV; + for (int tk = 0; tk < KV_TILE_SZ; tk++) { + const float p = KQ[tq * KV_TILE_SZ + tk]; + const float * v_row = (const float *)((const char *) v->data + ((ic + tk)*nbv1 + iv2*nbv2 + iv3*nbv3)); + ggml_vec_mad_f32(DV, vkq_row, v_row, p); + } + } + } + } + + // sinks (apply only to valid rows in the tile) + if (sinks) { + const float s = ((float *)((char *) sinks->data))[h]; + + for (int tq = 0; tq < tile_rows; tq++) { + float ms = 1.0f; + float vs = 1.0f; + + if (s > M[tq]) { + ms = expf(M[tq] - s); + ggml_vec_scale_f32(DV, VKQ32 + tq * DV, ms); + } else { + vs = expf(s - M[tq]); + } + + S[tq] = S[tq] * ms + vs; + } + } + + for (int tq = 0; tq < tile_rows; tq++) { + // V /= S + const float S_inv = S[tq] == 0.0f ? 0.0f : 1.0f / S[tq]; + ggml_vec_scale_f32(DV, VKQ32 + tq * DV, S_inv); + + // dst indices + const int i1 = iq1 + tq; + const int i2 = iq2; + const int i3 = iq3; + + // permute(0, 2, 1, 3) + memcpy((char *) dst->data + (i3*ne2*ne1 + i2 + i1*ne1)*nb1, VKQ32 + tq * DV, nb1); + } + + ir += tile_rows; + } +} + static void ggml_compute_forward_flash_attn_ext_f16( const ggml_compute_params * params, ggml_tensor * dst) { @@ -8343,6 +8618,15 @@ static void ggml_compute_forward_flash_attn_ext_f16( // The number of elements in each chunk const int64_t dr = (nr + nchunk - 1) / nchunk; + static constexpr int64_t KV_TILE_SZ = ggml_fa_tile_config::KV; + static constexpr int64_t Q_TILE_SZ = ggml_fa_tile_config::Q; + const bool kv_is_f32_or_f16 = (k->type == GGML_TYPE_F32 || k->type == GGML_TYPE_F16); + const bool use_tiled = (q->type == GGML_TYPE_F32 && + kv_is_f32_or_f16 && + k->type == v->type && + nek1 % KV_TILE_SZ == 0 && + neq1 >= Q_TILE_SZ); // Only use tiled for batch >= tile size + // The first chunk comes from our thread_id, the rest will get auto-assigned. int current_chunk = ith; @@ -8350,7 +8634,11 @@ static void ggml_compute_forward_flash_attn_ext_f16( const int64_t ir0 = dr * current_chunk; const int64_t ir1 = MIN(ir0 + dr, nr); - ggml_compute_forward_flash_attn_ext_f16_one_chunk(params, dst, ir0, ir1); + if (use_tiled) { + ggml_compute_forward_flash_attn_ext_tiled(params, dst, ir0, ir1); + } else { + ggml_compute_forward_flash_attn_ext_f16_one_chunk(params, dst, ir0, ir1); + } current_chunk = ggml_threadpool_chunk_add(params->threadpool, 1); }