[Multi Modal][Performance] Fused Q,K's apply_rope into one (#24511)

Signed-off-by: wwl2755 <wangwenlong2755@gmail.com>
Co-authored-by: Isotr0py <mozf@mail2.sysu.edu.cn>

vllm/model_executor/models/qwen2_5_vl.py

@@ -363,8 +363,10 @@ class Qwen2_5_VisionAttention(nn.Module):
         q, k, v = (rearrange(x, "s b ... -> b s ...").contiguous()
                    for x in (q, k, v))
         if rotary_pos_emb is not None:
-            q = apply_rotary_pos_emb_vision(q, rotary_pos_emb)
-            k = apply_rotary_pos_emb_vision(k, rotary_pos_emb)
+            # [2 * b, s, heads, head_dim]
+            qk_concat = torch.cat([q, k], dim=0)
+            qk_rotated = apply_rotary_pos_emb_vision(qk_concat, rotary_pos_emb)
+            q, k = torch.chunk(qk_rotated, 2, dim=0)
 
         if self.is_flash_attn_backend:
             if self.attn_backend == _Backend.ROCM_AITER_FA:
@@ -388,8 +390,8 @@ class Qwen2_5_VisionAttention(nn.Module):
                                             causal=False)
 
             context_layer = rearrange(output,
-                                      "(b s) ... -> b s ...",
-                                      b=batch_size)
+                                      "(b s) h d -> s b (h d)",
+                                      b=batch_size).contiguous()
         elif self.attn_backend == _Backend.TORCH_SDPA:
             # Execute attention entry by entry for speed & less VRAM.
             outputs = []
@@ -408,6 +410,8 @@ class Qwen2_5_VisionAttention(nn.Module):
                 output_i = rearrange(output_i, "b h s d -> b s h d ")
                 outputs.append(output_i)
             context_layer = torch.cat(outputs, dim=1)
+            context_layer = rearrange(context_layer,
+                                      "b s h d -> s b (h d)").contiguous()
         elif self.attn_backend == _Backend.XFORMERS:
             from xformers import ops as xops
             from xformers.ops.fmha.attn_bias import BlockDiagonalMask
@@ -418,8 +422,8 @@ class Qwen2_5_VisionAttention(nn.Module):
 
             context_layer = xops.memory_efficient_attention_forward(
                 q, k, v, attn_bias=attn_bias, p=0, scale=None)
-        context_layer = rearrange(context_layer,
-                                  "b s h d -> s b (h d)").contiguous()
+            context_layer = rearrange(context_layer,
+                                      "b s h d -> s b (h d)").contiguous()
 
         output, _ = self.proj(context_layer)
         return output