[Bugfix] Fix benchmark_fused_collective.py (#38082)

Signed-off-by: Jee Jee Li <pandaleefree@gmail.com>

benchmarks/kernels/benchmark_fused_collective.py

@@ -25,6 +25,7 @@ import pandas as pd
 import torch  # type: ignore
 import torch.distributed as dist  # type: ignore
 
+from vllm._custom_ops import create_fp4_output_tensors
 from vllm.config.vllm import CompilationConfig, VllmConfig, set_current_vllm_config
 from vllm.distributed import (
     tensor_model_parallel_all_reduce,
@@ -46,7 +47,7 @@ RMS_NORM_STATIC_FP8_QUANT_OP = torch.ops._C.rms_norm_static_fp8_quant
 FUSED_ADD_RMS_NORM_STATIC_FP8_QUANT_OP = (
     torch.ops._C.fused_add_rms_norm_static_fp8_quant
 )
-SCALED_FP4_QUANT_OP = torch.ops._C.scaled_fp4_quant
+SCALED_FP4_QUANT_OUT_OP = torch.ops._C.scaled_fp4_quant.out
 
 logger = init_logger(__name__)
 
@@ -334,13 +335,23 @@ class VllmFusedAllreduce:
         output_scale: torch.Tensor,
     ):
         allreduce_out = tensor_model_parallel_all_reduce(input_tensor)
-        rms_out = self.rms_norm(allreduce_out, residual)
+        rms_output = self.rms_norm(allreduce_out, residual)
+        if residual is None:
+            rms_out = rms_output
+        else:
+            rms_out, residual_out = rms_output
+
+        SCALED_FP4_QUANT_OUT_OP(
+            rms_out,
+            input_global_scale,
+            True,
+            output=quant_out,
+            output_scale=output_scale,
+        )
+
         if residual is None:
-            SCALED_FP4_QUANT_OP(quant_out, rms_out, output_scale, input_global_scale)
             return quant_out, output_scale
         else:
-            rms_out, residual_out = rms_out
-            SCALED_FP4_QUANT_OP(quant_out, rms_out, output_scale, input_global_scale)
             return quant_out, residual_out, output_scale
 
 
@@ -362,8 +373,9 @@ def create_test_tensors(
     scale_fp4 = torch.tensor(1.0, dtype=torch.float32)
     quant_out_fp8 = torch.empty_like(input_tensor, dtype=FP8_DTYPE)
     # Pre-allocate FP4 output tensors (to avoid allocation overhead in benchmarks)
-    fp4_quant_out = torch.empty((num_tokens, hidden_dim // 2), dtype=torch.uint8)
-    fp4_output_scale = torch.empty((128, 4), dtype=torch.int32)
+    fp4_quant_out, fp4_output_scale = create_fp4_output_tensors(
+        num_tokens, hidden_dim, input_tensor.device, True
+    )
 
     return (
         input_tensor,