[Scheduler] Add --max-low-priority-prefills scheduler gate for P0/P1 isolation - #3
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…isolation New SchedulerConfig field max_low_priority_prefills (default 0 = off). When > 0 and long_prefill_token_threshold is also set, the V1 WAITING admission loop counts how many RUNNING requests are still prefilling (num_computed_tokens < num_prompt_tokens) and have priority >= 1 (P1) and prompt_len > threshold. If that count >= limit, the waiting P1 long-prefill candidate is deferred to skipped_waiting rather than promoted to RUNNING, capping the aggregate token-budget consumed by concurrent low-priority prefills (N*C where N = concurrent P1s and C = per-request chunk cap) and preserving headroom for P0 traffic. Uses num_computed_tokens < num_prompt_tokens rather than is_prefill_chunk so the count is accurate for requests admitted earlier in the same loop iteration (is_prefill_chunk is stale until _update_after_schedule runs). Gate is placed after the LoRA check and before the expensive prefix-cache query to fail fast. AsyncScheduler needs no patching. CLI: --max-low-priority-prefills N Config: SchedulerConfig.max_low_priority_prefills Validation: raises if > 0 and long_prefill_token_threshold == 0. Signed-off-by: Procr <193802945+procr1337@users.noreply.github.com>
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v20-r7 rebase: https://github.com/procr1337/vllm/tree/feat/max-low-priority-prefill_v20-r7
New SchedulerConfig field max_low_priority_prefills (default 0 = off). When > 0 and long_prefill_token_threshold is also set, the V1 WAITING admission loop counts how many RUNNING requests are still prefilling (num_computed_tokens < num_prompt_tokens) and have priority >= 1 (P1) and prompt_len > threshold. If that count >= limit, the waiting P1 long-prefill candidate is deferred to skipped_waiting rather than promoted to RUNNING, capping the aggregate token-budget consumed by concurrent low-priority prefills (N*C where N = concurrent P1s and C = per-request chunk cap) and preserving headroom for P0 traffic.
Uses num_computed_tokens < num_prompt_tokens rather than is_prefill_chunk so the count is accurate for requests admitted earlier in the same loop iteration (is_prefill_chunk is stale until _update_after_schedule runs). Gate is placed after the LoRA check and before the expensive prefix-cache query to fail fast. AsyncScheduler needs no patching.
CLI:
--max-low-priority-prefills N --long-prefill-token-threshold MConfig: SchedulerConfig.max_low_priority_prefills
Validation: raises if > 0 and long_prefill_token_threshold == 0.