From e037ad90ed6ee06a1c32dabd962a615b7515e3fb Mon Sep 17 00:00:00 2001
From: Felicity Liao <felicity@meta.com>
Date: Tue, 11 Mar 2025 14:20:13 -0700
Subject: [PATCH] DO NOT LAND

Differential Revision: D70993764
---
 torchrec/distributed/model_parallel.py | 49 +++++++++-----------------
 1 file changed, 17 insertions(+), 32 deletions(-)

diff --git a/torchrec/distributed/model_parallel.py b/torchrec/distributed/model_parallel.py
index 1358def72..16b58c196 100644
--- a/torchrec/distributed/model_parallel.py
+++ b/torchrec/distributed/model_parallel.py
@@ -10,7 +10,7 @@
 import abc
 import copy
 import logging as logger
-from collections import defaultdict, OrderedDict
+from collections import OrderedDict
 from typing import Any, Callable, cast, Dict, Iterator, List, Optional, Set, Tuple, Type
 
 import torch
@@ -754,57 +754,42 @@ def sync(self, include_optimizer_state: bool = True) -> None:
             include_optimizer_state (bool): Flag to include optimizer state syncing upon call
         """
         assert self._replica_pg is not None, "replica_pg is not initialized!"
-        all_weights_by_dtype: dict[torch.dtype, List[torch.Tensor]] = defaultdict(list)
-
-        for emb_kernel in self._modules_to_sync:
+        all_weights: List[torch.Tensor] = [
+            w
+            for emb_kernel in self._modules_to_sync
             # pyre-fixme[29]: `Union[Module, Tensor]` is not a function.
-            for w in emb_kernel.split_embedding_weights():
-                all_weights_by_dtype[w.dtype].append(w)
+            for w in emb_kernel.split_embedding_weights()
+        ]
 
         opts = None
         if self._custom_all_reduce is None:
             opts = dist.AllreduceCoalescedOptions()
             opts.reduceOp = dist.ReduceOp.AVG
-        self._allreduce_tensors(all_weights_by_dtype, opts)
+        self._allreduce_tensors(all_weights, opts)
 
         if include_optimizer_state:
-            optimizer_tensors_by_dtype: Dict[torch.dtype, List[torch.Tensor]] = (
-                defaultdict(list)
-            )
+            optimizer_tensors = []
             for emb_kernel in self._modules_to_sync:
                 # pyre-fixme[29]: `Union[Module, Tensor]` is not a function.
                 optimizer_states = emb_kernel.get_optimizer_state()
-                for state in optimizer_states:
-                    opt_tensor = state["sum"]
-                    optimizer_tensors_by_dtype[opt_tensor.dtype].append(opt_tensor)
-            if optimizer_tensors_by_dtype:
-                self._allreduce_tensors(optimizer_tensors_by_dtype, opts)
+                optimizer_tensors.extend([state["sum"] for state in optimizer_states])
+            if optimizer_tensors:
+                self._allreduce_tensors(optimizer_tensors, opts)
 
     def _allreduce_tensors(
         self,
-        tensors_dict: Dict[torch.dtype, List[torch.Tensor]],
+        tensors: List[torch.Tensor],
         opts: Optional[dist.AllreduceCoalescedOptions] = None,
     ) -> None:
         """
         Helper to perform all reduce on given tensors, uses custom all reduce function if provided
-        We perform all reduce per tensor dtype per collective constraints.
         """
-
-        def custom_all_reduce(tensors: List[torch.Tensor]) -> None:
-            # pyre-ignore[29]
+        if self._custom_all_reduce is not None:
+            # pyre-ignore[6]
             self._custom_all_reduce(tensors)
-
-        def default_allreduce(tensor_list: List[torch.Tensor]) -> None:
-            self._replica_pg.allreduce_coalesced(tensor_list, opts=opts).wait()
-
-        allreduce = (
-            custom_all_reduce
-            if self._custom_all_reduce is not None
-            else default_allreduce
-        )
-
-        for tensor_list in tensors_dict.values():
-            allreduce(tensor_list)
+        else:
+            handle = self._replica_pg.allreduce_coalesced(tensors, opts=opts)
+            handle.wait()
 
     def set_all_reduce_hook(
         self,