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cutlass/examples/88_hopper_fmha/reference/fmha_bwd_reference.hpp
2025-06-06 02:39:20 -04:00

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/***************************************************************************************************
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* SPDX-License-Identifier: BSD-3-Clause
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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*
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#pragma once
#include "cute/tensor.hpp"
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
class TensorDQ, /* class TensorDK, class TensorDV, */
class Fusion
>
void __global__ fmha_bwd_reference_dQ_kernel(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
TensorDQ mDQ, /* TensorDK mDK, TensorDV mDV, */
Fusion fusion
) {
using namespace cute;
using Element = typename TensorO::value_type;
using ElementAccumulator = typename TensorLSE::value_type;
extern __shared__ char mS_mem[];
Element* mS = reinterpret_cast<Element*>(mS_mem);
Element softmax_scale = static_cast<Element>(1.0 / sqrt(1.0 * size<1>(mO)));
for (int idx_L = blockIdx.y; idx_L < size<2>(mDQ); idx_L += gridDim.y) {
for (int idx_Q = blockIdx.x; idx_Q < size<0>(mDQ); idx_Q += gridDim.x) {
for (int idx_K = threadIdx.x; idx_K < size<0>(mK); idx_K += blockDim.x) {
ElementAccumulator acc_qk = 0;
ElementAccumulator acc_dov = 0;
ElementAccumulator acc_doo = 0;
for (int idx_D0 = 0; idx_D0 < size<1>(mK); idx_D0++) {
acc_qk += mQ(idx_Q, idx_D0, idx_L) * mK(idx_K, idx_D0, idx_L);
acc_dov += mDO(idx_Q, idx_D0, idx_L) * mV(idx_K, idx_D0, idx_L);
acc_doo += mDO(idx_Q, idx_D0, idx_L) * mO(idx_Q, idx_D0, idx_L);
}
auto id = make_identity_tensor(make_shape(1, 1));
auto frag = make_tensor<ElementAccumulator>(Shape<_1, _1>{});
frag(0) = acc_qk;
fusion.before_softmax(frag, make_tensor(id.data() + make_arithmetic_tuple(idx_Q, idx_K), id.layout()), problem_shape);
acc_qk = frag(0);
mS[idx_K] = static_cast<Element>(exp(softmax_scale * acc_qk - mLSE(idx_Q, idx_L)) * softmax_scale * (acc_dov - acc_doo));
}
__syncthreads();
for (int idx_D = threadIdx.x; idx_D < size<1>(mDQ); idx_D += blockDim.x) {
ElementAccumulator acc = 0;
for (int idx_K = 0; idx_K < size<0>(mK); idx_K++) {
acc += mS[idx_K] * mK(idx_K, idx_D, idx_L);
}
mDQ(idx_Q, idx_D, idx_L) = acc;
}
}
}
}
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
/* class TensorDQ, */ class TensorDK, /* class TensorDV, */
class Fusion
>
void __global__ fmha_bwd_reference_dK_kernel(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
/* TensorDQ mDQ, */ TensorDK mDK, /* TensorDV mDV, */
Fusion fusion
) {
using namespace cute;
using Element = typename TensorO::value_type;
using ElementAccumulator = typename TensorLSE::value_type;
extern __shared__ char mS_mem[];
Element* mS = reinterpret_cast<Element*>(mS_mem);
Element softmax_scale = static_cast<Element>(1.0 / sqrt(1.0 * size<1>(mO)));
for (int idx_L = blockIdx.y; idx_L < size<2>(mDK); idx_L += gridDim.y) {
for (int idx_K = blockIdx.x; idx_K < size<0>(mDK); idx_K += gridDim.x) {
for (int idx_Q = threadIdx.x; idx_Q < size<0>(mDO); idx_Q += blockDim.x) {
ElementAccumulator acc_qk = 0;
ElementAccumulator acc_dov = 0;
ElementAccumulator acc_doo = 0;
for (int idx_D0 = 0; idx_D0 < size<1>(mK); idx_D0++) {
acc_qk += mQ(idx_Q, idx_D0, idx_L) * mK(idx_K, idx_D0, idx_L);
acc_dov += mDO(idx_Q, idx_D0, idx_L) * mV(idx_K, idx_D0, idx_L);
acc_doo += mDO(idx_Q, idx_D0, idx_L) * mO(idx_Q, idx_D0, idx_L);
}
auto id = make_identity_tensor(make_shape(1, 1));
auto frag = make_tensor<ElementAccumulator>(Shape<_1, _1>{});
frag(0) = acc_qk;
fusion.before_softmax(frag, make_tensor(id.data() + make_arithmetic_tuple(idx_Q, idx_K), id.layout()), problem_shape);
acc_qk = frag(0);
mS[idx_Q] = static_cast<Element>(exp(softmax_scale * acc_qk - mLSE(idx_Q, idx_L)) * softmax_scale * (acc_dov - acc_doo));
}
__syncthreads();
for (int idx_D = threadIdx.x; idx_D < size<1>(mDK); idx_D += blockDim.x) {
ElementAccumulator acc = 0;
for (int idx_Q = 0; idx_Q < size<0>(mDO); idx_Q++) {
acc += mS[idx_Q] * mQ(idx_Q, idx_D, idx_L);
}
mDK(idx_K, idx_D, idx_L) = acc;
}
}
}
}
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
/* class TensorDQ, class TensorDK, */ class TensorDV,
class Fusion
>
void __global__ fmha_bwd_reference_dV_kernel(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
/* TensorDQ mDQ, TensorDK mDK, */ TensorDV mDV,
Fusion fusion
) {
using namespace cute;
using Element = typename TensorO::value_type;
using ElementAccumulator = typename TensorLSE::value_type;
extern __shared__ char mS_mem[];
Element* mS = reinterpret_cast<Element*>(mS_mem);
Element softmax_scale = static_cast<Element>(1.0 / sqrt(1.0 * size<1>(mO)));
for (int idx_L = blockIdx.y; idx_L < size<2>(mDV); idx_L += gridDim.y) {
for (int idx_K = blockIdx.x; idx_K < size<0>(mDV); idx_K += gridDim.x) {
for (int idx_Q = threadIdx.x; idx_Q < size<0>(mDO); idx_Q += blockDim.x) {
ElementAccumulator acc_qk = 0;
for (int idx_D0 = 0; idx_D0 < size<1>(mK); idx_D0++) {
acc_qk += mQ(idx_Q, idx_D0, idx_L) * mK(idx_K, idx_D0, idx_L);
}
auto id = make_identity_tensor(make_shape(1, 1));
auto frag = make_tensor<ElementAccumulator>(Shape<_1, _1>{});
frag(0) = acc_qk;
fusion.before_softmax(frag, make_tensor(id.data() + make_arithmetic_tuple(idx_Q, idx_K), id.layout()), problem_shape);
acc_qk = frag(0);
mS[idx_Q] = static_cast<Element>(exp(softmax_scale * acc_qk - mLSE(idx_Q, idx_L)));
}
__syncthreads();
for (int idx_D = threadIdx.x; idx_D < size<1>(mDV); idx_D += blockDim.x) {
ElementAccumulator acc = 0;
for (int idx_Q = 0; idx_Q < size<0>(mDO); idx_Q++) {
acc += mS[idx_Q] * mDO(idx_Q, idx_D, idx_L);
}
mDV(idx_K, idx_D, idx_L) = acc;
}
}
}
}
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
/**/ class TensorDQ, /** / class TensorDK, / ** / class TensorDV, / **/
class Fusion
>
void fmha_bwd_reference_dQ(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
/**/ TensorDQ mDQ, /** / TensorDK mDK, / ** / TensorDV mDV, / **/
Fusion fusion
) {
using namespace cute;
dim3 grid(size<0>(mDQ), size<2>(mDQ), 1);
dim3 block(256);
int shared_mem = size<0>(mK) * sizeof(typename TensorO::value_type);
if (shared_mem >= (48 << 10)) {
CUTLASS_TRACE_HOST(" Setting smem size to " << shared_mem);
auto result = cudaFuncSetAttribute(
fmha_bwd_reference_dQ_kernel<ProblemShape, TensorQ, TensorK, TensorV, TensorO, TensorLSE, TensorDO, TensorDQ, Fusion>,
cudaFuncAttributeMaxDynamicSharedMemorySize,
shared_mem);
if (cudaSuccess != result) {
result = cudaGetLastError(); // to clear the error bit
CUTLASS_TRACE_HOST(
" cudaFuncSetAttribute() returned error: "
<< cudaGetErrorString(result));
return;
}
}
fmha_bwd_reference_dQ_kernel<<<grid, block, shared_mem>>>(problem_shape, mQ, mK, mV, mO, mLSE, mDO, mDQ, fusion);
}
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
/** / class TensorDQ, / **/ class TensorDK, /** / class TensorDV, / **/
class Fusion
>
void fmha_bwd_reference_dK(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
/** / TensorDQ mDQ, / **/ TensorDK mDK, /** / TensorDV mDV, / **/
Fusion fusion
) {
using namespace cute;
dim3 grid(size<0>(mDK), size<2>(mDK), 1);
dim3 block(256);
int shared_mem = size<0>(mDO) * sizeof(typename TensorO::value_type);
if (shared_mem >= (48 << 10)) {
CUTLASS_TRACE_HOST(" Setting smem size to " << shared_mem);
auto result = cudaFuncSetAttribute(
fmha_bwd_reference_dK_kernel<ProblemShape, TensorQ, TensorK, TensorV, TensorO, TensorLSE, TensorDO, TensorDK, Fusion>,
cudaFuncAttributeMaxDynamicSharedMemorySize,
shared_mem);
if (cudaSuccess != result) {
result = cudaGetLastError(); // to clear the error bit
CUTLASS_TRACE_HOST(
" cudaFuncSetAttribute() returned error: "
<< cudaGetErrorString(result));
return;
}
}
fmha_bwd_reference_dK_kernel<<<grid, block, shared_mem>>>(problem_shape, mQ, mK, mV, mO, mLSE, mDO, mDK, fusion);
}
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
/** / class TensorDQ, / ** / class TensorDK, / **/ class TensorDV, /**/
class Fusion
>
void fmha_bwd_reference_dV(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
/** / TensorDQ mDQ, / ** / TensorDK mDK, / **/ TensorDV mDV, /**/
Fusion fusion
) {
using namespace cute;
dim3 grid(size<0>(mDV), size<2>(mDV), 1);
dim3 block(256);
int shared_mem = size<0>(mDO) * sizeof(typename TensorO::value_type);
if (shared_mem >= (48 << 10)) {
CUTLASS_TRACE_HOST(" Setting smem size to " << shared_mem);
auto result = cudaFuncSetAttribute(
fmha_bwd_reference_dV_kernel<ProblemShape, TensorQ, TensorK, TensorV, TensorO, TensorLSE, TensorDO, TensorDV, Fusion>,
cudaFuncAttributeMaxDynamicSharedMemorySize,
shared_mem);
if (cudaSuccess != result) {
result = cudaGetLastError(); // to clear the error bit
CUTLASS_TRACE_HOST(
" cudaFuncSetAttribute() returned error: "
<< cudaGetErrorString(result));
return;
}
}
fmha_bwd_reference_dV_kernel<<<grid, block, shared_mem>>>(problem_shape, mQ, mK, mV, mO, mLSE, mDO, mDV, fusion);
}
/////////////////////////////////////////////////////////////////////////////////////////////////
template<
class ProblemShape,
class TensorQ, class TensorK, class TensorV,
class TensorO, class TensorLSE, class TensorDO,
class TensorDQ, class TensorDK, class TensorDV,
class Fusion
>
void fmha_bwd_reference(
ProblemShape problem_shape,
TensorQ mQ, TensorK mK, TensorV mV,
TensorO mO, TensorLSE mLSE, TensorDO mDO,
TensorDQ mDQ, TensorDK mDK, TensorDV mDV,
Fusion fusion
) {
fmha_bwd_reference_dQ(problem_shape, mQ, mK, mV, mO, mLSE, mDO, mDQ, fusion);
fmha_bwd_reference_dK(problem_shape, mQ, mK, mV, mO, mLSE, mDO, mDK, fusion);
fmha_bwd_reference_dV(problem_shape, mQ, mK, mV, mO, mLSE, mDO, mDV, fusion);
}
/////////////////////////////////////////////////////////////////////////////////////////////////