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[BugFix] port finding and avoid hardcoded ipv4 host #10693

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[BugFix] port finding and avoid hardcoded ipv4 host #10693

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379f824
[BugFix] find port deadlock and nccl_port repeat
xk-huang Sep 17, 2025
7333ce5
[BugFix] avoid hard code ipv4 host for dist init
xk-huang Sep 20, 2025
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2 changes: 1 addition & 1 deletion python/sglang/srt/model_executor/model_runner.py
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Original file line number Diff line number Diff line change
Expand Up @@ -621,7 +621,7 @@ def init_torch_distributed(self):
if self.server_args.dist_init_addr:
dist_init_method = f"tcp://{self.server_args.dist_init_addr}"
else:
dist_init_method = f"tcp://127.0.0.1:{self.dist_port}"
dist_init_method = f"tcp://{self.server_args.host}:{self.dist_port}"
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@gemini-code-assist gemini-code-assist bot Sep 20, 2025

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high

This change correctly replaces the hardcoded 127.0.0.1 with self.server_args.host. However, if self.server_args.host is an IPv6 address, it needs to be enclosed in square brackets (e.g., [::1]) to form a valid TCP URL for torch.distributed. Without the brackets, initialization will fail for IPv6 hosts. It's recommended to handle this case.

Suggested change
dist_init_method = f"tcp://{self.server_args.host}:{self.dist_port}"
host = self.server_args.host
if ":" in host and not host.startswith("["):
# Wrap IPv6 addresses in brackets for URL formatting.
host = f"[{host}]"
dist_init_method = f"tcp://{host}:{self.dist_port}"

set_custom_all_reduce(not self.server_args.disable_custom_all_reduce)
set_mscclpp_all_reduce(self.server_args.enable_mscclpp)

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7 changes: 6 additions & 1 deletion python/sglang/srt/server_args.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2788,9 +2788,14 @@ def init_new(server_args, dp_rank: Optional[int] = None) -> "PortArgs":
if nccl_port < 60000:
nccl_port += 42
else:
nccl_port -= 43
nccl_port = server_args.port + random.randint(100, 1000)
Comment on lines 2788 to +2791
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medium

The logic for finding an available port when one is not provided is a bit complex. Using nccl_port += 42 is arbitrary, and re-randomizing the port if it's above 60000 can lead to new collisions between processes. A simpler and more robust approach would be to use a linear probe (nccl_port += 1), which is consistent with the logic used when nccl_port is provided by the user. This ensures deterministic port finding after the initial random selection.

                nccl_port += 1

else:
nccl_port = server_args.nccl_port
# Check if the port is available
while True:
if is_port_available(nccl_port):
break
nccl_port += 1

if not server_args.enable_dp_attention:
# Normal case, use IPC within a single node
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