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[Kernel] Remove redundant Exp calculations (#16123)

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Signed-off-by: DefTruth <qiustudent_r@163.com>
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DefTruth 2025-04-15 20:58:37 +08:00 committed by GitHub
parent 1666e66443
commit 280d62b8a2
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1 changed files with 6 additions and 3 deletions
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9
vllm/attention/ops/triton_merge_attn_states.py
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@ -66,7 +66,10 @@ def merge_attn_states_kernel(
max_lse = tl.maximum(p_lse, s_lse)
p_lse = p_lse - max_lse
s_lse = s_lse - max_lse
out_se = (tl.exp(p_lse) + tl.exp(s_lse))
# Will reuse precomputed Exp values for scale factor computation.
p_se = tl.exp(p_lse)
s_se = tl.exp(s_lse)
out_se = (p_se + s_se)
if OUTPUT_LSE:
out_lse = tl.log(out_se) + max_lse
@ -84,8 +87,8 @@ def merge_attn_states_kernel(
# NOTE(woosuk): Be careful with the numerical stability.
# We should compute the scale first, and then multiply it with the output.
# Do not multiply the output with tl.exp(p_lse) or tl.exp(s_lse) directly.
p_scale = tl.exp(p_lse) / out_se
s_scale = tl.exp(s_lse) / out_se
p_scale = p_se / out_se
s_scale = s_se / out_se
out = p_out * p_scale + s_out * s_scale
tl.store(output + token_idx * num_heads * HEAD_SIZE +
head_idx * HEAD_SIZE + head_arange,