[Misc] Add attention mask pre-computation optimization back to Qwen2.5-VL (#15273)

Signed-off-by: Isotr0py <2037008807@qq.com>

vllm/model_executor/models/qwen2_5_vl.py

@@ -608,6 +608,17 @@ class Qwen2_5_VisionTransformer(nn.Module):
         window_index = torch.cat(window_index, dim=0)
         return window_index, cu_window_seqlens
 
+    def compute_attn_mask_seqlen(
+        self,
+        cu_seqlens: torch.Tensor,
+    ) -> tuple[Optional[int], Optional[list[int]]]:
+        max_seqlen, seqlens = None, None
+        if self.attn_backend == _Backend.FLASH_ATTN:
+            max_seqlen = (cu_seqlens[1:] - cu_seqlens[:-1]).max().item()
+        elif self.attn_backend == _Backend.XFORMERS:
+            seqlens = (cu_seqlens[1:] - cu_seqlens[:-1]).tolist()
+        return max_seqlen, seqlens
+
     def forward(
         self,
         x: torch.Tensor,
@@ -645,25 +656,27 @@ class Qwen2_5_VisionTransformer(nn.Module):
         # transformers
         hidden_states = hidden_states.unsqueeze(1)
 
-        max_seqlen = None
-        seqlens = None
+        # pre-compute seqlens for window/full attn to reduce cuMemcpy operations
+        max_seqlen_full, seqlens_full = self.compute_attn_mask_seqlen(
+            cu_seqlens)
+        max_seqlen_window, seqlens_window = self.compute_attn_mask_seqlen(
+            cu_window_seqlens)
         for layer_num, blk in enumerate(self.blocks):
             if layer_num in self.fullatt_block_indexes:
                 cu_seqlens_now = cu_seqlens
+                max_seqlen_now = max_seqlen_full
+                seqlens_now = seqlens_full
             else:
                 cu_seqlens_now = cu_window_seqlens
-            # pre-compute cu_seqlens for window attn
-            if self.attn_backend == _Backend.FLASH_ATTN:
-                max_seqlen = (cu_seqlens_now[1:] -
-                              cu_seqlens_now[:-1]).max().item()
-            elif self.attn_backend == _Backend.XFORMERS:
-                seqlens = (cu_seqlens_now[1:] - cu_seqlens_now[:-1]).tolist()
+                max_seqlen_now = max_seqlen_window
+                seqlens_now = seqlens_window
+
             hidden_states = blk(
                 hidden_states,
                 cu_seqlens=cu_seqlens_now,
                 rotary_pos_emb=rotary_pos_emb,
-                max_seqlen=max_seqlen,
-                seqlens=seqlens,
+                max_seqlen=max_seqlen_now,
+                seqlens=seqlens_now,
             )
 
         # For Qwen2.5-VL-3B, float16 will overflow at last block

vllm/model_executor/models/qwen2_vl.py

@@ -617,6 +617,16 @@ class Qwen2VisionTransformer(nn.Module):
         rotary_pos_emb = rotary_pos_emb_full[pos_ids].flatten(1)
         return rotary_pos_emb
 
+    def compute_attn_mask_seqlen(
+            self, cu_seqlens: torch.Tensor
+    ) -> tuple[Optional[int], Optional[list[int]]]:
+        max_seqlen, seqlens = None, None
+        if self.attn_backend == _Backend.FLASH_ATTN:
+            max_seqlen = (cu_seqlens[1:] - cu_seqlens[:-1]).max().item()
+        elif self.attn_backend == _Backend.XFORMERS:
+            seqlens = (cu_seqlens[1:] - cu_seqlens[:-1]).tolist()
+        return max_seqlen, seqlens
+
     def forward(
         self,
         x: torch.Tensor,
@@ -638,12 +648,8 @@ class Qwen2VisionTransformer(nn.Module):
         # transformers
         x = x.unsqueeze(1)
 
-        max_seqlen = None
-        seqlens = None
-        if self.attn_backend == _Backend.FLASH_ATTN:
-            max_seqlen = (cu_seqlens[1:] - cu_seqlens[:-1]).max().item()
-        elif self.attn_backend == _Backend.XFORMERS:
-            seqlens = (cu_seqlens[1:] - cu_seqlens[:-1]).tolist()
+        # pre-compute seqlens for attn mask to reduce cuMemcpy operations
+        max_seqlen, seqlens = self.compute_attn_mask_seqlen(cu_seqlens)
         for blk in self.blocks:
             x = blk(
                 x,