From 8fcc69e7c473318b54ae33e5b1f805baa654589f Mon Sep 17 00:00:00 2001
From: Chunyuan WU <chunyuan.wu@intel.com>
Date: Sat, 18 Oct 2025 03:35:20 +0800
Subject: [PATCH] Turn on shm_allreduce and shm_allgather for fp16 (#10725)

---
 python/sglang/srt/utils/common.py |   2 +-
 test/srt/cpu/test_comm.py         | 118 ++++++++++++++++++++++++++++++
 2 files changed, 119 insertions(+), 1 deletion(-)
 create mode 100644 test/srt/cpu/test_comm.py

diff --git a/python/sglang/srt/utils/common.py b/python/sglang/srt/utils/common.py
index 084065b61..51ee7d10e 100644
--- a/python/sglang/srt/utils/common.py
+++ b/python/sglang/srt/utils/common.py
@@ -2921,7 +2921,7 @@ def get_cpu_ids_by_node():
 def is_shm_available(dtype, world_size, local_size):
     return (
         cpu_has_amx_support()
-        and dtype in [torch.bfloat16, torch.float]
+        and dtype in [torch.bfloat16, torch.float16, torch.float]
         and world_size >= 1
         and world_size == local_size
     )
diff --git a/test/srt/cpu/test_comm.py b/test/srt/cpu/test_comm.py
new file mode 100644
index 000000000..60e7194bd
--- /dev/null
+++ b/test/srt/cpu/test_comm.py
@@ -0,0 +1,118 @@
+import copy
+import multiprocessing
+import os
+import traceback
+import unittest
+from multiprocessing import Process
+
+import sgl_kernel
+import torch
+import torch.distributed as dist
+import torch.multiprocessing as mp
+from utils import precision
+
+from sglang.test.test_utils import CustomTestCase, find_available_port
+
+
+def run_distributed_test(rank, world_size, master_port, output_writer, fn):
+    try:
+        os.environ["RANK"] = str(rank)
+        os.environ["WORLD_SIZE"] = str(world_size)
+        os.environ["MASTER_ADDR"] = "localhost"
+        os.environ["MASTER_PORT"] = str(master_port)
+        os.environ["LOCAL_SIZE"] = str(world_size)
+
+        dist.init_process_group("gloo", rank=rank, world_size=world_size)
+        torch.ops.sgl_kernel.initialize(world_size, rank)
+
+        fn(rank, world_size)
+
+        execution_ok = True
+    except Exception as e:
+        print(f"subprocess[{rank=}] has error: {e}", flush=True)
+        traceback.print_exc()
+        execution_ok = False
+
+    output_writer.send(execution_ok)
+    output_writer.close()
+
+    if dist.is_initialized():
+        dist.destroy_process_group()
+
+
+def all_reduce_fn(rank, world_size):
+    op = dist.ReduceOp.SUM
+    for dtype in [torch.float32, torch.bfloat16, torch.float16]:
+        tensor = torch.randn(2, 10, dtype=dtype)
+        tensor_shm = copy.deepcopy(tensor)
+
+        dist.all_reduce(tensor, op=op)
+        torch.ops.sgl_kernel.shm_allreduce(tensor_shm, op)
+
+        torch.testing.assert_close(tensor, tensor_shm)
+
+
+def all_gather_fn(rank, world_size):
+    dim = -1
+
+    for dtype in [torch.float32, torch.bfloat16, torch.float16]:
+        tensor = torch.randn(2, 10, dtype=dtype)
+
+        if dim < 0:
+            # Convert negative dim to positive.
+            dim += tensor.dim()
+
+        input_size = tensor.size()
+        output_size = (input_size[0] * world_size,) + input_size[1:]
+        output_tensor = torch.empty(
+            output_size, dtype=tensor.dtype, device=tensor.device
+        )
+        dist.all_gather_into_tensor(output_tensor, tensor)
+        output_tensor = output_tensor.reshape((world_size,) + input_size)
+        output_tensor = output_tensor.movedim(0, dim)
+        output_tensor = output_tensor.reshape(
+            input_size[:dim] + (world_size * input_size[dim],) + input_size[dim + 1 :]
+        )
+
+        output_shm = torch.ops.sgl_kernel.shm_allgather(tensor, dim)
+
+        torch.testing.assert_close(output_tensor, output_shm)
+
+
+class TestComm(CustomTestCase):
+    def _spawn_and_check(self, fn, world_size=2):
+        mp.set_start_method("spawn", force=True)
+        master_port = find_available_port(23456)
+
+        processes = []
+        output_reader, output_writer = multiprocessing.Pipe(duplex=False)
+
+        for rank in range(world_size):
+            p = Process(
+                target=run_distributed_test,
+                kwargs=dict(
+                    rank=rank,
+                    world_size=world_size,
+                    master_port=master_port,
+                    output_writer=output_writer,
+                    fn=fn,
+                ),
+            )
+            p.start()
+            processes.append(p)
+
+        for _ in range(world_size):
+            self.assertTrue(output_reader.recv(), "Subprocess fail. Check logs above.")
+
+        for p in processes:
+            p.join()
+
+    def test_all_reduce(self):
+        self._spawn_and_check(all_reduce_fn)
+
+    def test_all_gather(self):
+        self._spawn_and_check(all_gather_fn)
+
+
+if __name__ == "__main__":
+    unittest.main()