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[BugFix]Fix the issue where there is no parallelism in PP mode #28286

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[BugFix]Fix the issue where there is no parallelism in PP mode #28286

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7 changes: 6 additions & 1 deletion vllm/v1/core/sched/scheduler.py
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Original file line number Diff line number Diff line change
Expand Up @@ -397,7 +397,12 @@ def schedule(self) -> SchedulerOutput:
while self.waiting and token_budget > 0:
if len(self.running) == self.max_num_running_reqs:
break

if len(scheduled_resumed_reqs) + len(scheduled_new_reqs) >= max(
1,
self.max_num_running_reqs
// self.parallel_config.pipeline_parallel_size,
):
break
Comment on lines +400 to +405
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@gemini-code-assist gemini-code-assist bot Nov 7, 2025

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critical

The division by self.parallel_config.pipeline_parallel_size on line 361 assumes this value is non-zero. If it were misconfigured to be 0, this would lead to a ZeroDivisionError, causing the scheduler to crash. While pipeline_parallel_size defaults to 1, adding a check to ensure it's positive would make the code more robust against configuration errors. The suggested change also improves readability by extracting the limit into a variable.

Suggested change
if len(scheduled_resumed_reqs) + len(scheduled_new_reqs) >= max(
1,
self.max_num_running_reqs
// self.parallel_config.pipeline_parallel_size,
):
break
pp_size = self.parallel_config.pipeline_parallel_size
if pp_size <= 0:
raise ValueError(
"pipeline_parallel_size must be positive, but is "
f"{pp_size}")
limit = max(1, self.max_num_running_reqs // pp_size)
if len(scheduled_resumed_reqs) + len(scheduled_new_reqs) >= limit:
break

request = self.waiting.peek_request()

# KVTransfer: skip request if still waiting for remote kvs.
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