vllm-project/vllm

[Feature]: Priority scheduling supports preemption of requests in the running queue by requests in the waiting queue

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#40,004 opened on Apr 16, 2026

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 (6 comments) (0 reactions) (0 assignees)Python (16,816 forks)batch import
feature requesthelp wanted

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Description

🚀 The feature, motivation and pitch

The current priority scheduling only supports evicting low-priority requests from the running queue when resources are insufficient. However, when scheduling the waiting queue, if pending requests cannot be scheduled (for example, when the number of requests in the running queue has reached max_num_seqs), even high-priority requests cannot preempt requests in the running queue.

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Contributor guide

Research direction
Study the current priority scheduling implementation in vllm/vllm/core/scheduler.py and the waiting/run queue logic. Identify where to add preemption logic to allow high priority waiting requests to preempt low priority running requests.
Tech stack
python
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Python
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60