fix missing function in blocking_copy (meta-pytorch#3492)

Summary:
Pull Request resolved: meta-pytorch#3492

# context
* somehow the blocking_copy function is missed from previous diff: D85508674
* added it back

Reviewed By: aporialiao

Differential Revision: D85774050

fbshipit-source-id: 58e798d611eb0000bf2fde815745f834e3c5cd46

Author: TroyGarden

torchrec/distributed/benchmark/benchmark_comms.py

@@ -483,11 +483,14 @@ def non_blocking_copy(
     num_concat: int,
     ctx: MultiProcessContext,
     preallocated: bool = False,
+    use_data_copy_stream: bool = True,
     **_kwargs: Dict[str, Any],
 ) -> None:
     with record_function("## setup ##"):
         main_stream = torch.cuda.current_stream()
-        data_copy_stream = torch.cuda.Stream()
+        data_copy_stream = (
+            torch.cuda.Stream() if use_data_copy_stream else nullcontext()
+        )
         irrelevant_data = torch.rand(dim, dim, device=ctx.device) - 0.5
 
         # the host to device data transfer will block cuda execution without the `pin_memory()`
@@ -519,7 +522,8 @@ def non_blocking_copy(
 
     with record_function("## pre-comms compute ##"):
         # make sure the data copy is done before the pre-comms compute
-        main_stream.wait_stream(data_copy_stream)
+        if use_data_copy_stream:
+            main_stream.wait_stream(data_copy_stream)
         pre_comms = _compute(
             dim=dim, num_mul=num_mul, num_concat=1, ctx=ctx, x=device_data
         )
@@ -543,6 +547,24 @@ def preallocated_non_blocking_copy(
     )
 
 
+def blocking_copy(
+    _batch_inputs: List[Dict[str, Any]],
+    dim: int,
+    num_mul: int,
+    num_concat: int,
+    ctx: MultiProcessContext,
+    **_kwargs: Dict[str, Any],
+) -> None:
+    return non_blocking_copy(
+        _batch_inputs=_batch_inputs,
+        dim=dim,
+        num_mul=num_mul,
+        num_concat=num_concat,
+        ctx=ctx,
+        use_data_copy_stream=False,
+    )
+
+
 # single-rank runner
 def a2a_single_runner(rank: int, world_size: int, arg: AllToAllSingleRunConfig) -> None:
     # Ensure GPUs are available and we have enough of them
@@ -576,6 +598,8 @@ def a2a_single_runner(rank: int, world_size: int, arg: AllToAllSingleRunConfig)
                 func = non_blocking_copy
             case "preallocated_non_blocking_copy":
                 func = preallocated_non_blocking_copy
+            case "blocking_copy":
+                func = blocking_copy
             case _:
                 raise ValueError(f"Unknown benchmark name: {arg.name}")