Remove copy after bmm (sgl-project#7441)

Author: ispobock

python/sglang/srt/models/deepseek_v2.py

@@ -1084,13 +1084,16 @@ def forward_absorb_core(
                 masked_m,
                 expected_m,
             )
-            attn_bmm_output = attn_bmm_output[:, :expected_m, :]
+            attn_bmm_output = (
+                attn_bmm_output[:, :expected_m, :].transpose(0, 1).flatten(1, 2)
+            )
         elif _is_hip:
             # TODO(haishaw): add bmm_fp8 to ROCm
             attn_bmm_output = torch.bmm(
                 attn_output.to(torch.bfloat16).transpose(0, 1),
                 self.w_vc.to(torch.bfloat16) * self.w_scale,
             )
+            attn_bmm_output = attn_bmm_output.transpose(0, 1).flatten(1, 2)
         elif self.w_vc.dtype == torch.float8_e4m3fn:
             attn_output_val, attn_output_scale = per_tensor_quant_mla_fp8(
                 attn_output.transpose(0, 1),
@@ -1103,10 +1106,21 @@ def forward_absorb_core(
                 self.w_scale,
                 torch.bfloat16,
             )
+            attn_bmm_output = attn_bmm_output.transpose(0, 1).flatten(1, 2)
         else:
-            attn_bmm_output = torch.bmm(attn_output.transpose(0, 1), self.w_vc)
-        attn_output = attn_bmm_output.transpose(0, 1).flatten(1, 2)
-        output, _ = self.o_proj(attn_output)
+            attn_bmm_output = torch.empty(
+                (attn_output.shape[0], self.num_local_heads * self.v_head_dim),
+                dtype=attn_output.dtype,
+                device=attn_output.device,
+            )
+            torch.bmm(
+                attn_output.transpose(0, 1),
+                self.w_vc,
+                out=attn_bmm_output.view(
+                    -1, self.num_local_heads, self.v_head_dim
+                ).transpose(0, 1),
+            )
+        output, _ = self.o_proj(attn_bmm_output)
 
         return output