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[Fix] Select custom all-reduce v2 by topology capability (#35061)

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Co-authored-by: xingyuliu <xingyuliu@fb.com>
This commit is contained in:
Xingyu Liu
2026-08-18 10:30:10 -07:00
committed by GitHub
co-authored by xingyuliu
parent 480033def0
commit 7dcaf11987
8 changed files with 268 additions and 236 deletions
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python/sglang/srt/server_args.py
-36
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@@ -8026,41 +8026,6 @@ class ServerArgs:
"1" if requested_transport == "cuda_ipc" else "0"
)
def _handle_custom_all_reduce_v2_multinode(self):
# Custom all-reduce v2's graph zero-copy path uses IPC handles and is
# intra-node only. On MNNVL-fabric devices (GB200/GB300) the eager pull
# path works across nodes via the symm-mem workspace, so opt into the
# multinode mode automatically (a failed fabric rendezvous falls back
# to the legacy path at init). Elsewhere force-disable v2 on
# multi-node so the dispatch falls back to the legacy CustomAllreduce
# path, unless the MNNVL opt-in is set explicitly.
if self.nnodes <= 1 or not envs.SGLANG_OPT_USE_CUSTOM_ALL_REDUCE_V2.get():
return
if (
not envs.SGLANG_ENABLE_CUSTOM_ALL_REDUCE_V2_MULTINODE.is_set()
and is_mnnvl_fabric_device()
# CustomAllReduceV2 supports world sizes 2..8 only
# (can_use_custom_all_reduce_v2 rejects larger groups); don't
# auto-opt-in a TP16+ launch just to fall back downstream.
and self.tp_size <= 8
):
logger.info(
"MNNVL fabric device detected with nnodes=%d: enabling "
"custom all-reduce v2 multinode mode "
"(SGLANG_ENABLE_CUSTOM_ALL_REDUCE_V2_MULTINODE=1; set it "
"to 0 to opt out).",
self.nnodes,
)
envs.SGLANG_ENABLE_CUSTOM_ALL_REDUCE_V2_MULTINODE.set("1")
if not envs.SGLANG_ENABLE_CUSTOM_ALL_REDUCE_V2_MULTINODE.get():
if envs.SGLANG_OPT_USE_CUSTOM_ALL_REDUCE_V2.is_set():
logger.warning(
"Disabling SGLANG_OPT_USE_CUSTOM_ALL_REDUCE_V2 because nnodes=%d "
"(custom all-reduce v2 is intra-node only).",
self.nnodes,
)
envs.SGLANG_OPT_USE_CUSTOM_ALL_REDUCE_V2.set("0")
def _handle_environment_variables(self):
self._handle_multimodal_feature_transport()
envs.SGLANG_ENABLE_TORCH_COMPILE.set("1" if self.enable_torch_compile else "0")
@@ -8072,7 +8037,6 @@ class ServerArgs:
envs.SGLANG_ENABLE_DETERMINISTIC_INFERENCE.set(
"1" if self.enable_deterministic_inference else "0"
)
self._handle_custom_all_reduce_v2_multinode()
if self.enable_deterministic_inference:
envs.SGLANG_FLASHINFER_MOE_FUSED_FINALIZE.set("0")
if self.debug_cuda_graph: