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Enhance bias gradient accumulation in backward pass #193
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
|
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@@ -159,6 +159,10 @@ inline __device__ void compute_dq_dk_dv_1colblock(const Params ¶ms, const in | |
| Shape<Int<kBlockM>, Int<kBlockN>>{}, | ||
| make_stride(params.dbias_row_stride, _1{}) | ||
| ); | ||
| [[maybe_unused]] ElementAccum *gdBias_accum_ptr = nullptr; | ||
| if constexpr (Has_bias) { | ||
| gdBias_accum_ptr = reinterpret_cast<ElementAccum *>(params.dbias_ptr) + row_offset_dbias; | ||
| } | ||
| Tensor gdO = make_tensor( | ||
| make_gmem_ptr(reinterpret_cast<Element *>(params.do_ptr) + row_offset_do), | ||
| Shape<Int<kBlockM>, Int<kHeadDim>>{}, | ||
|
|
@@ -848,12 +852,37 @@ inline __device__ void compute_dq_dk_dv_1colblock(const Params ¶ms, const in | |
| __syncthreads(); | ||
| if constexpr (Has_bias) { | ||
| // Write dS to dBias | ||
| FLASH_NAMESPACE::copy_MN<Is_even_MN, /*Clear_OOB_MN=*/false>( | ||
| gmem_tiled_copy_dBias, | ||
| tBiassBias, tdBiasgdBias, | ||
| tBiascBias, tBiaspBias, | ||
| binfo.actual_seqlen_q - m_block * kBlockM | ||
| ); | ||
| if (!params.accum_dbias) { | ||
| FLASH_NAMESPACE::copy_MN<Is_even_MN, /*Clear_OOB_MN=*/false>( | ||
| gmem_tiled_copy_dBias, | ||
| tBiassBias, tdBiasgdBias, | ||
| tBiascBias, tBiaspBias, | ||
| binfo.actual_seqlen_q - m_block * kBlockM | ||
| ); | ||
| } else { | ||
| #pragma unroll | ||
| for (int m = 0; m < size<1>(tBiassBias); ++m) { | ||
| if (Is_even_MN || get<0>(tBiascBias(0, m, 0)) < binfo.actual_seqlen_q - m_block * kBlockM) { | ||
| #pragma unroll | ||
| for (int n = 0; n < size<2>(tBiassBias); ++n) { | ||
| if (Is_even_MN || tBiaspBias(n)) { | ||
| #pragma unroll | ||
| for (int i = 0; i < size<0>(tBiassBias); ++i) { | ||
| const auto coord = tBiascBias(i, m, n); | ||
| const int row = get<0>(coord); | ||
| const int col = get<1>(coord); | ||
| if (Is_even_MN || row < binfo.actual_seqlen_q - m_block * kBlockM) { | ||
| atomicAdd( | ||
| gdBias_accum_ptr + row * params.dbias_row_stride + col, | ||
| static_cast<ElementAccum>(tBiassBias(i, m, n)) | ||
| ); | ||
| } | ||
| } | ||
| } | ||
|
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||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // if (cute::thread0()) { print(tPrP); } | ||
|
|
@@ -994,6 +1023,9 @@ inline __device__ void compute_dq_dk_dv_1colblock(const Params ¶ms, const in | |
| // Advance gBias and gdBias | ||
| tBiasgBias.data() = tBiasgBias.data() + (-int(kBlockM * params.bias_row_stride)); | ||
| tdBiasgdBias.data() = tdBiasgdBias.data() + (-int(kBlockM * params.dbias_row_stride)); | ||
| if (params.accum_dbias) { | ||
| gdBias_accum_ptr -= int(kBlockM * params.dbias_row_stride); | ||
| } | ||
| if (any_active_next) { | ||
| FLASH_NAMESPACE::copy_MN<Is_even_MN, /*Clear_OOB_MN=*/true>( | ||
| gmem_tiled_copy_Bias, | ||
|
|
||
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The new condition only allocates an expanded buffer when batch_size_bias == 1 or seqlen_q_bias == 1 (broadcast), but drops the previous handling for general mismatches (batch_size_bias != batch_size or seqlen_q_bias != seqlen_q where the size is not 1). This can cause the kernel to write into a tensor with incompatible shape/strides when dbias dimensions mismatch but are not broadcastable (e.g., batch_size_bias=2 vs batch_size=4, seqlen_q_bias=64 vs seqlen_q=128). Restore the general mismatch allocation while keeping the float accumulation path for seqlen_q_bias == 1. For example, keep the outer mismatch check as (num_heads_bias != num_heads || batch_size_bias != batch_size || seqlen_q_bias != seqlen_q) and specialize the inner allocation to use float only when seqlen_q_bias == 1.