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Fix stride issues in flash_attn_interface #58

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Fix stride issues in flash_attn_interface #58

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530f407
Fix stride issue in flash_attn_interface
clintg6 May 29, 2024
363d82e
restore empty_like
clintg6 May 31, 2024
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10 changes: 8 additions & 2 deletions flash_attn/flash_attn_interface.py
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Original file line number Diff line number Diff line change
Expand Up @@ -60,9 +60,15 @@ def _flash_attn_varlen_forward(q, k, v, cu_seqlens_q, cu_seqlens_k, max_seqlen_q

def _flash_attn_backward(dout, q, k, v, out, softmax_lse, dq, dk, dv,
dropout_p, softmax_scale, causal, rng_state=None):
maybe_contiguous = lambda x: x.contiguous() if x.stride(-1) != 1 else x
maybe_contiguous = lambda x: x.contiguous() if not x.is_contiguous() else x
# dq, dk, dv are allocated by us so they should already be contiguous
dout, q, k, v, out = [maybe_contiguous(x) for x in (dout, q, k, v, out)]

if out.stride() != dout.stride():
out = out.as_strided(dout.size(),dout.stride())
if dq.stride() != q.stride():
dq = dq.as_strided(q.size(),q.stride())

dq, dk, dv, softmax_d, = flash_attn_cuda.bwd(
dout, q, k, v, out, softmax_lse, dq, dk, dv, dropout_p,
softmax_scale, causal, None, rng_state
Expand All @@ -73,7 +79,7 @@ def _flash_attn_backward(dout, q, k, v, out, softmax_lse, dq, dk, dv,
def _flash_attn_varlen_backward(dout, q, k, v, out, softmax_lse, dq, dk, dv,
cu_seqlens_q, cu_seqlens_k, max_seqlen_q, max_seqlen_k,
dropout_p, softmax_scale, causal, rng_state=None):
maybe_contiguous = lambda x: x.contiguous() if x.stride(-1) != 1 else x
maybe_contiguous = lambda x: x.contiguous() if not x.is_contiguous() else x
# dq, dk, dv are allocated by us so they should already be contiguous
dout, q, k, v, out = [maybe_contiguous(x) for x in (dout, q, k, v, out)]
dq, dk, dv, softmax_d, = flash_attn_cuda.varlen_bwd(
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