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add exclusive self attention.

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This commit is contained in:
Rohan Khan 2026-04-12 18:32:55 +06:00
parent a445144d39
commit 7ecaf86519
1 changed files with 12 additions and 2 deletions
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14
nanochat/flash_attention.py
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@ -117,7 +117,10 @@ def flash_attn_func(q, k, v, causal=False, window_size=(-1, -1)):
Output tensor of shape (B, T, H, D)
"""
if USE_FA3:
return _fa3.flash_attn_func(q, k, v, causal=causal, window_size=window_size)
y = _fa3.flash_attn_func(q, k, v, causal=causal, window_size=window_size)
Vn = F.normalize(v, dim=-1)
y = y - (y * Vn).sum(dim=-1, keepdim=True) * Vn
return y
# SDPA fallback: transpose (B, T, H, D) -> (B, H, T, D)
q = q.transpose(1, 2)
@ -125,6 +128,8 @@ def flash_attn_func(q, k, v, causal=False, window_size=(-1, -1)):
v = v.transpose(1, 2)
enable_gqa = q.size(1) != k.size(1)
y = _sdpa_attention(q, k, v, window_size, enable_gqa)
Vn = F.normalize(v, dim=-1)
y = y - (y * Vn).sum(dim=-1, keepdim=True) * Vn
return y.transpose(1, 2) # back to (B, T, H, D)
@ -147,10 +152,13 @@ def flash_attn_with_kvcache(q, k_cache, v_cache, k=None, v=None, cache_seqlens=N
Output tensor of shape (B, T_new, H, D)
"""
if USE_FA3:
return _fa3.flash_attn_with_kvcache(
y = _fa3.flash_attn_with_kvcache(
q, k_cache, v_cache, k=k, v=v, cache_seqlens=cache_seqlens,
causal=causal, window_size=window_size
)
Vn = F.normalize(v, dim=-1)
y = y - (y * Vn).sum(dim=-1, keepdim=True) * Vn
return y
# SDPA fallback: manually manage KV cache
B, T_new, H, D = q.shape
@ -173,6 +181,8 @@ def flash_attn_with_kvcache(q, k_cache, v_cache, k=None, v=None, cache_seqlens=N
enable_gqa = q_sdpa.size(1) != k_sdpa.size(1)
y_sdpa = _sdpa_attention(q_sdpa, k_sdpa, v_sdpa, window_size, enable_gqa)
Vn = F.normalize(v_sdpa, dim=-1)
y_sdpa = y_sdpa - (y_sdpa * Vn).sum(dim=-1, keepdim=True) * Vn
return y_sdpa.transpose(1, 2) # back to (B, T, H, D)