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CUDA: generalize FP16 fattn vec kernel (#7061)

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* CUDA: generalize FP16 fattn vec kernel

* disable unsupported head sizes for AMD in test

* try AMD fix

* fix batch size 2-8

* partially revert changes
This commit is contained in:
Johannes Gäßler 2024-05-09 14:32:02 +02:00 • committed by GitHub
parent f31ec120bc
commit a743d76a01
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4 changed files with 374 additions and 220 deletions
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331
ggml-cuda/fattn.cu
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@ -11,8 +11,10 @@
#define HALF_MAX_HALF __float2half(65504.0f/2) // Use neg. of this instead of -INFINITY to initialize KQ max vals to avoid NaN upon subtraction.
#define SOFTMAX_FTZ_THRESHOLD -20.0f // Softmax exp. of values smaller than this are flushed to zero to avoid NaNs.
template<int D, int parallel_blocks> // D == head size
__launch_bounds__(((D + WARP_SIZE - 1) / WARP_SIZE)*WARP_SIZE, 1)
template<int D, int ncols, int parallel_blocks> // D == head size
#if !(defined(GGML_USE_HIPBLAS) && defined(__HIP_PLATFORM_AMD__))
__launch_bounds__(D, 1)
#endif // !(defined(GGML_USE_HIPBLAS) && defined(__HIP_PLATFORM_AMD__))
static __global__ void flash_attn_vec_ext_f16(
const char * __restrict__ Q,
const char * __restrict__ K,
@ -44,55 +46,77 @@ static __global__ void flash_attn_vec_ext_f16(
#if FP16_AVAILABLE
//In this kernel Q, K, V are matrices while i, j, k are matrix indices.
const int ic = blockIdx.x / parallel_blocks; // Index of the Q/QKV column to work on.
const int ip = blockIdx.x % parallel_blocks; // Index in group of blocks running for the same column in parallel.
const int ic0 = (blockIdx.x / parallel_blocks) * ncols; // Index of the Q/QKV column to work on.
const int ip = blockIdx.x % parallel_blocks; // Index in group of blocks running for the same column in parallel.
const int gqa_ratio = ne02 / ne12; // With grouped query attention there are > 1 Q matrices per K, V matrix.
const float2 * Q_f2 = (const float2 *) (Q + nb02* blockIdx.y + nb01*ic);
const float2 * Q_f2 = (const float2 *) (Q + nb02* blockIdx.y + nb01*ic0);
const half2 * K_h2 = (const half2 *) (K + nb12*(blockIdx.y / gqa_ratio));
const half * V_h = (const half *) (V + nb12*(blockIdx.y / gqa_ratio)); // K and V have same shape
const half * maskh = (const half *) mask + ne11*ic;
const half * maskh = (const half *) mask + ne11*ic0;
const int stride_KV = nb11 / sizeof(half);
const int stride_KV2 = nb11 / sizeof(half2);
constexpr int nwarps = (D + WARP_SIZE - 1) / WARP_SIZE;
static_assert(D % (2*WARP_SIZE) == 0, "D not divisible by 2*WARP_SIZE == 64.");
constexpr int nwarps = D / WARP_SIZE;
const int tid = WARP_SIZE*threadIdx.y + threadIdx.x;
__builtin_assume(tid < nwarps*WARP_SIZE);
__builtin_assume(tid < D);
__shared__ half KQ[nwarps*WARP_SIZE];
KQ[tid] = -INFINITY;
__shared__ half KQ[ncols*D];
#pragma unroll
for (int j = 0; j < ncols; ++j) {
KQ[j*D + tid] = -HALF_MAX_HALF;
}
half2 * KQ2 = (half2 *) KQ;
half kqmax = -HALF_MAX_HALF;
half kqsum = 0.0f;
half kqmax[ncols];
#pragma unroll
for (int j = 0; j < ncols; ++j) {
kqmax[j] = -HALF_MAX_HALF;
}
half kqsum[ncols] = {0.0f};
__shared__ half kqmax_shared[WARP_SIZE];
__shared__ half kqsum_shared[WARP_SIZE];
if (threadIdx.y == 0) {
kqmax_shared[threadIdx.x] = -HALF_MAX_HALF;
kqsum_shared[threadIdx.x] = 0.0f;
__shared__ half kqmax_shared[ncols][WARP_SIZE];
__shared__ half kqsum_shared[ncols][WARP_SIZE];
#pragma unroll
for (int j = 0; j < ncols; ++j) {
if (threadIdx.y == 0) {
kqmax_shared[j][threadIdx.x] = -HALF_MAX_HALF;
kqsum_shared[j][threadIdx.x] = 0.0f;
}
}
__syncthreads();
// Convert Q to half2 and store in registers:
half2 Q_h2[(D/2 + WARP_SIZE - 1) / WARP_SIZE];
half2 Q_h2[ncols][D/(2*WARP_SIZE)];
#pragma unroll
for (int i0 = 0; i0 < D/2; i0 += WARP_SIZE) {
const int i = i0 + threadIdx.x;
if (i0 + WARP_SIZE > D/2 && i >= D/2) {
break;
}
for (int j = 0; j < ncols; ++j) {
#pragma unroll
for (int i0 = 0; i0 < D/2; i0 += WARP_SIZE) {
const int i = i0 + threadIdx.x;
Q_h2[i0/WARP_SIZE] = make_half2(scale, scale) * make_half2(Q_f2[i].x, Q_f2[i].y);
const float2 tmp = Q_f2[j*(nb01/sizeof(float2)) + i];
Q_h2[j][i0/WARP_SIZE] = make_half2(scale, scale) * make_half2(tmp.x, tmp.y);
}
}
half2 VKQ = make_half2(0.0f, 0.0f); // Each thread calculates a single VKQ value.
half2 VKQ[ncols] = {{0.0f, 0.0f}};
const int k_start = parallel_blocks == 1 ? 0 : ip*D;
const int k_start = parallel_blocks == 1 ? 0 : ip*D;
for (int k_VKQ_0 = k_start; k_VKQ_0 < ne11; k_VKQ_0 += parallel_blocks*D) {
// Calculate KQ tile and keep track of new maximum KQ values:
half kqmax_new = kqmax;
// For unknown reasons using a half array of size 1 for kqmax_new causes a performance regression,
// see https://github.com/ggerganov/llama.cpp/pull/7061 .
// Therefore this variable is defined twice but only used once (so that the compiler can optimize out the unused variable).
half kqmax_new = kqmax[0];
half kqmax_new_arr[ncols];
#pragma unroll
for (int j = 0; j < ncols; ++j) {
kqmax_new_arr[j] = kqmax[j];
}
#pragma unroll
for (int i_KQ_0 = 0; i_KQ_0 < D; i_KQ_0 += nwarps) {
const int i_KQ = i_KQ_0 + threadIdx.y;
@ -101,89 +125,112 @@ static __global__ void flash_attn_vec_ext_f16(
break;
}
half2 sum2 = make_half2(0.0f, 0.0f);
half2 sum2[ncols] = {{0.0f, 0.0f}};
#pragma unroll
for (int k_KQ_0 = 0; k_KQ_0 < D/2; k_KQ_0 += WARP_SIZE) {
const int k_KQ = k_KQ_0 + threadIdx.x;
if (k_KQ_0 + WARP_SIZE > D/2 && k_KQ >= D/2) {
break;
}
const half2 K_ik = K_h2[(k_VKQ_0 + i_KQ)*stride_KV2 + k_KQ];
sum2 += K_ik * Q_h2[k_KQ_0/WARP_SIZE];
}
sum2 = warp_reduce_sum(sum2);
half sum = __low2half(sum2) + __high2half(sum2);
sum += mask ? maskh[k_VKQ_0 + i_KQ] : __float2half(0.0f);
kqmax_new = ggml_cuda_hmax(kqmax_new, sum);
if (threadIdx.x == 0) {
KQ[i_KQ] = sum;
}
}
kqmax_new = warp_reduce_max(kqmax_new);
if (threadIdx.x == 0) {
kqmax_shared[threadIdx.y] = kqmax_new;
}
__syncthreads();
kqmax_new = kqmax_shared[threadIdx.x];
kqmax_new = warp_reduce_max(kqmax_new);
const half KQ_max_scale = hexp(kqmax - kqmax_new);
kqmax = kqmax_new;
const half val = hexp(KQ[tid] - kqmax);
kqsum = kqsum*KQ_max_scale + val;
KQ[tid] = val;
VKQ *= __half2half2(KQ_max_scale);
__syncthreads();
if (tid < D) {
#pragma unroll
for (int k0 = 0; k0 < D; k0 += 2) {
if (FATTN_KQ_STRIDE % D != 0 && k_VKQ_0 + k0 >= ne11) {
break;
for (int j = 0; j < ncols; ++j) {
sum2[j] += K_ik * Q_h2[j][k_KQ_0/WARP_SIZE];
}
}
#pragma unroll
for (int j = 0; j < ncols; ++j) {
sum2[j] = warp_reduce_sum(sum2[j]);
half sum = __low2half(sum2[j]) + __high2half(sum2[j]);
sum += mask ? maskh[j*ne11 + k_VKQ_0 + i_KQ] : __float2half(0.0f);
if (ncols == 1) {
kqmax_new = ggml_cuda_hmax(kqmax_new, sum);
} else {
kqmax_new_arr[j] = ggml_cuda_hmax(kqmax_new_arr[j], sum);
}
half2 V_k;
reinterpret_cast<half&>(V_k.x) = V_h[(k_VKQ_0 + k0 + 0)*stride_KV + tid];
reinterpret_cast<half&>(V_k.y) = V_h[(k_VKQ_0 + k0 + 1)*stride_KV + tid];
VKQ += V_k*KQ2[k0/2];
if (threadIdx.x == 0) {
KQ[j*D + i_KQ] = sum;
}
}
}
#pragma unroll
for (int j = 0; j < ncols; ++j) {
half kqmax_new_j = ncols == 1 ? kqmax_new : kqmax_new_arr[j];
kqmax_new_j = warp_reduce_max(kqmax_new_j);
if (threadIdx.x == 0) {
kqmax_shared[j][threadIdx.y] = kqmax_new_j;
}
}
__syncthreads();
#pragma unroll
for (int j = 0; j < ncols; ++j) {
half kqmax_new_j = kqmax_shared[j][threadIdx.x];
kqmax_new_j = warp_reduce_max(kqmax_new_j);
const half KQ_max_scale = hexp(kqmax[j] - kqmax_new_j);
kqmax[j] = kqmax_new_j;
const half val = hexp(KQ[j*D + tid] - kqmax[j]);
kqsum[j] = kqsum[j]*KQ_max_scale + val;
KQ[j*D + tid] = val;
VKQ[j] *= __half2half2(KQ_max_scale);
}
__syncthreads();
#pragma unroll
for (int k0 = 0; k0 < D; k0 += 2) {
if (FATTN_KQ_STRIDE % D != 0 && k_VKQ_0 + k0 >= ne11) {
break;
}
half2 V_k;
reinterpret_cast<half&>(V_k.x) = V_h[(k_VKQ_0 + k0 + 0)*stride_KV + tid];
reinterpret_cast<half&>(V_k.y) = V_h[(k_VKQ_0 + k0 + 1)*stride_KV + tid];
#pragma unroll
for (int j = 0; j < ncols; ++j) {
VKQ[j] += V_k*KQ2[j*(D/2) + k0/2];
}
}
__syncthreads();
}
if (tid >= D) {
kqsum = 0.0f;
#pragma unroll
for (int j = 0; j < ncols; ++j) {
kqsum[j] = warp_reduce_sum(kqsum[j]);
if (threadIdx.x == 0) {
kqsum_shared[j][threadIdx.y] = kqsum[j];
}
}
kqsum = warp_reduce_sum(kqsum);
if (threadIdx.x == 0) {
kqsum_shared[threadIdx.y] = kqsum;
}
__syncthreads();
kqsum = kqsum_shared[threadIdx.x];
kqsum = warp_reduce_sum(kqsum);
if (tid >= D) {
return;
#pragma unroll
for (int j_VKQ = 0; j_VKQ < ncols; ++j_VKQ) {
kqsum[j_VKQ] = kqsum_shared[j_VKQ][threadIdx.x];
kqsum[j_VKQ] = warp_reduce_sum(kqsum[j_VKQ]);
half dst_val = (__low2half(VKQ[j_VKQ]) + __high2half(VKQ[j_VKQ]));
if (parallel_blocks == 1) {
dst_val /= kqsum[j_VKQ];
}
const int j_dst = (ic0 + j_VKQ)*parallel_blocks + ip;
dst[j_dst*D*gridDim.y + D*blockIdx.y + tid] = dst_val;
}
half dst_val = (__low2half(VKQ) + __high2half(VKQ));
if (parallel_blocks == 1) {
dst_val /= kqsum;
if (parallel_blocks != 1 && tid != 0) {
#pragma unroll
for (int j = 0; j < ncols; ++j) {
dst_meta[(ic0 + j)*gridDim.y*parallel_blocks + blockIdx.y*parallel_blocks + ip] = make_float2(kqmax[j], kqsum[j]);
}
}
dst[D*gridDim.y*blockIdx.x + D*blockIdx.y + tid] = dst_val;
if (parallel_blocks == 1 || tid != 0) {
return;
}
dst_meta[ic*gridDim.y*parallel_blocks + blockIdx.y*parallel_blocks + ip] = make_float2(kqmax, kqsum);
#else
NO_DEVICE_CODE;
#endif // FP16_AVAILABLE
@ -191,7 +238,9 @@ static __global__ void flash_attn_vec_ext_f16(
// D == head size, VKQ_stride == num VKQ rows calculated in parallel:
template<int D, int ncols, int nwarps, int VKQ_stride, int parallel_blocks, typename KQ_acc_t>
#if !(defined(GGML_USE_HIPBLAS) && defined(__HIP_PLATFORM_AMD__))
__launch_bounds__(nwarps*WARP_SIZE, 1)
#endif // !(defined(GGML_USE_HIPBLAS) && defined(__HIP_PLATFORM_AMD__))
static __global__ void flash_attn_ext_f16(
const char * __restrict__ Q,
const char * __restrict__ K,
@ -573,7 +622,9 @@ static __global__ void flash_attn_ext_f16(
}
template<int D, int parallel_blocks> // D == head size
#if !(defined(GGML_USE_HIPBLAS) && defined(__HIP_PLATFORM_AMD__))
__launch_bounds__(D, 1)
#endif // !(defined(GGML_USE_HIPBLAS) && defined(__HIP_PLATFORM_AMD__))
static __global__ void flash_attn_combine_results(
const float * __restrict__ VKQ_parts,
const float2 * __restrict__ VKQ_meta,
@ -642,7 +693,7 @@ static_assert(get_VKQ_stride( 80, 1, 16) == 16, "Test failed.");
static_assert(get_VKQ_stride( 80, 2, 16) == 16, "Test failed.");
static_assert(get_VKQ_stride( 80, 4, 16) == 16, "Test failed.");
template <int D, int parallel_blocks> void launch_fattn_vec_f16(
template <int D, int cols_per_block, int parallel_blocks> void launch_fattn_vec_f16(
const ggml_tensor * Q, const ggml_tensor * K, const ggml_tensor * V, ggml_tensor * KQV, const ggml_tensor * mask,
ggml_cuda_pool & pool, cudaStream_t main_stream
) {
@ -656,13 +707,13 @@ template <int D, int parallel_blocks> void launch_fattn_vec_f16(
constexpr int nwarps = (D + WARP_SIZE - 1) / WARP_SIZE;
const dim3 block_dim(WARP_SIZE, nwarps, 1);
const dim3 blocks_num(parallel_blocks*Q->ne[1], Q->ne[2], Q->ne[3]);
const dim3 blocks_num(parallel_blocks*((Q->ne[1] + cols_per_block - 1) / cols_per_block), Q->ne[2], Q->ne[3]);
const int shmem = 0;
float scale;
memcpy(&scale, KQV->op_params, sizeof(float));
flash_attn_vec_ext_f16<D, parallel_blocks>
flash_attn_vec_ext_f16<D, cols_per_block, parallel_blocks>
<<<blocks_num, block_dim, shmem, main_stream>>> (
(const char *) Q->data,
(const char *) K->data,
@ -783,10 +834,99 @@ void ggml_cuda_flash_attn_ext(ggml_backend_cuda_context & ctx, ggml_tensor * dst
ggml_cuda_set_device(ctx.device);
const int cc = ggml_cuda_info().devices[ggml_cuda_get_device()].cc;
const int nsm = ggml_cuda_info().devices[ggml_cuda_get_device()].nsm;
const int32_t precision = KQV->op_params[1];
if (!fp16_mma_available(cc)) {
GGML_ASSERT(precision == GGML_PREC_DEFAULT);
GGML_ASSERT(Q->ne[0] == 64 || Q->ne[0] == 128 && "FlashAttention without tensor cores only supports head sizes 64 and 128.");
if (Q->ne[1] == 1) {
constexpr int cols_per_block = 1;
constexpr int parallel_blocks = 4;
switch (Q->ne[0]) {
case 64:
launch_fattn_vec_f16< 64, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 128:
launch_fattn_vec_f16<128, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
default:
GGML_ASSERT(false);
break;
}
return;
}
if (Q->ne[1] == 2) {
constexpr int cols_per_block = 2;
constexpr int parallel_blocks = 4;
switch (Q->ne[0]) {
case 64:
launch_fattn_vec_f16< 64, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 128:
launch_fattn_vec_f16<128, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
default:
GGML_ASSERT(false);
break;
}
return;
}
if (Q->ne[1] <= 4) {
constexpr int cols_per_block = 4;
constexpr int parallel_blocks = 4;
switch (Q->ne[0]) {
case 64:
launch_fattn_vec_f16< 64, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 128:
launch_fattn_vec_f16<128, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
default:
GGML_ASSERT(false);
break;
}
return;
}
if (Q->ne[1] <= 8) {
constexpr int cols_per_block = 8;
constexpr int parallel_blocks = 4;
switch (Q->ne[0]) {
case 64:
launch_fattn_vec_f16< 64, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 128:
launch_fattn_vec_f16<128, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
default:
GGML_ASSERT(false);
break;
}
return;
}
constexpr int cols_per_block = 8;
constexpr int parallel_blocks = 1;
switch (Q->ne[0]) {
case 64:
launch_fattn_vec_f16< 64, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 128:
launch_fattn_vec_f16<128, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
default:
GGML_ASSERT(false);
break;
}
return;
}
if (precision != GGML_PREC_DEFAULT) {
if (Q->ne[1] <= 32 || Q->ne[0] > 128) {
constexpr int cols_per_block = 16;
@ -845,16 +985,17 @@ void ggml_cuda_flash_attn_ext(ggml_backend_cuda_context & ctx, ggml_tensor * dst
}
if (Q->ne[1] == 1 && Q->ne[0] % (2*WARP_SIZE) == 0) {
constexpr int cols_per_block = 1;
constexpr int parallel_blocks = 4;
switch (Q->ne[0]) {
case 64:
launch_fattn_vec_f16< 64, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
launch_fattn_vec_f16< 64, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 128:
launch_fattn_vec_f16<128, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
launch_fattn_vec_f16<128, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
case 256:
launch_fattn_vec_f16<256, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
launch_fattn_vec_f16<256, cols_per_block, parallel_blocks>(Q, K, V, KQV, mask, ctx.pool(), ctx.stream());
break;
default:
GGML_ASSERT(false);