using sdpa if available (#2359)

* using sdpa if available

* Update model.py

whisper/model.py

@@ -1,7 +1,8 @@
 import base64
 import gzip
+from contextlib import contextmanager
 from dataclasses import dataclass
-from typing import Dict, Iterable, Optional
+from typing import Dict, Iterable, Optional, Tuple
 
 import numpy as np
 import torch
@@ -12,6 +13,14 @@
 from .decoding import detect_language as detect_language_function
 from .transcribe import transcribe as transcribe_function
 
+try:
+    from torch.nn.functional import scaled_dot_product_attention
+
+    SDPA_AVAILABLE = True
+except (ImportError, RuntimeError, OSError):
+    scaled_dot_product_attention = None
+    SDPA_AVAILABLE = False
+
 
 @dataclass
 class ModelDimensions:
@@ -59,7 +68,19 @@ def sinusoids(length, channels, max_timescale=10000):
     return torch.cat([torch.sin(scaled_time), torch.cos(scaled_time)], dim=1)
 
 
+@contextmanager
+def disable_sdpa():
+    prev_state = MultiHeadAttention.use_sdpa
+    try:
+        MultiHeadAttention.use_sdpa = False
+        yield
+    finally:
+        MultiHeadAttention.use_sdpa = prev_state
+
+
 class MultiHeadAttention(nn.Module):
+    use_sdpa = True
+
     def __init__(self, n_state: int, n_head: int):
         super().__init__()
         self.n_head = n_head
@@ -92,20 +113,30 @@ def forward(
 
     def qkv_attention(
         self, q: Tensor, k: Tensor, v: Tensor, mask: Optional[Tensor] = None
-    ):
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         n_batch, n_ctx, n_state = q.shape
         scale = (n_state // self.n_head) ** -0.25
-        q = q.view(*q.shape[:2], self.n_head, -1).permute(0, 2, 1, 3) * scale
-        k = k.view(*k.shape[:2], self.n_head, -1).permute(0, 2, 3, 1) * scale
+        q = q.view(*q.shape[:2], self.n_head, -1).permute(0, 2, 1, 3)
+        k = k.view(*k.shape[:2], self.n_head, -1).permute(0, 2, 1, 3)
         v = v.view(*v.shape[:2], self.n_head, -1).permute(0, 2, 1, 3)
 
-        qk = q @ k
-        if mask is not None:
-            qk = qk + mask[:n_ctx, :n_ctx]
-        qk = qk.float()
+        if SDPA_AVAILABLE and MultiHeadAttention.use_sdpa:
+            a = scaled_dot_product_attention(
+                q, k, v, is_causal=mask is not None and n_ctx > 1
+            )
+            out = a.permute(0, 2, 1, 3).flatten(start_dim=2)
+            qk = None
+        else:
+            qk = (q * scale) @ (k * scale).transpose(-1, -2)
+            if mask is not None:
+                qk = qk + mask[:n_ctx, :n_ctx]
+            qk = qk.float()
+
+            w = F.softmax(qk, dim=-1).to(q.dtype)
+            out = (w @ v).permute(0, 2, 1, 3).flatten(start_dim=2)
+            qk = qk.detach()
 
-        w = F.softmax(qk, dim=-1).to(q.dtype)
-        return (w @ v).permute(0, 2, 1, 3).flatten(start_dim=2), qk.detach()
+        return out, qk
 
 
 class ResidualAttentionBlock(nn.Module):

whisper/timing.py

@@ -191,7 +191,9 @@ def find_alignment(
         for i, block in enumerate(model.decoder.blocks)
     ]
 
-    with torch.no_grad():
+    from .model import disable_sdpa
+
+    with torch.no_grad(), disable_sdpa():
         logits = model(mel.unsqueeze(0), tokens.unsqueeze(0))[0]
         sampled_logits = logits[len(tokenizer.sot_sequence) :, : tokenizer.eot]
         token_probs = sampled_logits.softmax(dim=-1)