e4f726fc44
* hard-code alibi in fwd * use params.h as hun_heads * hard-code alibi in bwd * add alibi on/off option * compute alibi_start, ratio outside of kernels * fix minor merge conflict * add test_alibi.py * change apply_alibi() location before masking * add alibi in splitkv kernel * fix backward func # of returns * add out-of-bound check in apply_alibi() * update test_alibi.py * update test_alibi.py for kvcache * simplify alibi parameter interface * fix performance issue by computing alibi outside of branch * update test_flash_attn_varlen_func() for left padding * implement alibi_slopes (b, nh) loading * optimize apply_alibi() a bit * update test cases for alibi_slopes loading * reflect stylistic comments * disable "seqlenq_ngroups_swapped" when using alibi --------- Co-authored-by: monk.detective <monk.detective@kakaobrain.com>
54 lines
2.1 KiB
C++
54 lines
2.1 KiB
C++
#include <cmath>
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#include <cute/tensor.hpp>
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#include <cutlass/cutlass.h>
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#include <cutlass/array.h>
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#include "utils.h"
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namespace flash {
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using namespace cute;
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////////////////////////////////////////////////////////////////////////////////////////////////////
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template <typename Engine, typename Layout>
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inline __device__ void apply_alibi(Tensor<Engine, Layout> &tensor,
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const int col_idx_offset_,
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const int max_seqlen_k,
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const int row_idx_offset_,
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const int max_seqlen_q,
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const int warp_row_stride,
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const int head_idx,
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const float softmax_scale,
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const float alibi_slope) {
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// tensor has shape (ncol=(2, MMA_M), nrow=(2, MMA_N))
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static_assert(Layout::rank == 2, "Only support 2D Tensor");
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const int lane_id = threadIdx.x % 32;
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const int row_idx_offset = row_idx_offset_;
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const int col_idx_offset = col_idx_offset_ + (lane_id % 4) * 2;
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const float alibi_slope_unscaled = alibi_slope / softmax_scale;
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#pragma unroll
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for (int mi = 0; mi < size<0, 1>(tensor); ++mi) {
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const int row_idx_base = row_idx_offset + mi * warp_row_stride;
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#pragma unroll
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for (int i = 0; i < size<0, 0>(tensor); ++i) {
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const int row_idx = row_idx_base + i * 8;
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#pragma unroll
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for (int nj = 0; nj < size<1, 1>(tensor); ++nj) {
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const int col_idx_base = col_idx_offset + nj * 8;
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#pragma unroll
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for (int j = 0; j < size<1, 0>(tensor); ++j) {
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const int col_idx = col_idx_base + j;
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const float alibi = alibi_slope_unscaled * col_idx;
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if (col_idx < max_seqlen_k && row_idx < max_seqlen_q) {
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tensor(make_coord(i, mi), make_coord(j, nj)) += alibi;
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}
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}
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}
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}
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}
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}
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} // namespace flash
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