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Avoid refilling a different static-buffer slot when the number of offloaded modules is not divisible by the prefetch step. Add focused coverage for divisible, non-divisible, and trivial ring shapes. Signed-off-by: Big2Wheel <1404207590@qq.com>
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✅ @Big2Wheel, CI is now available for this PR.
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Repository UI Review profile: CHILL Plan: Team Run ID: 📒 Files selected for processing (2)
Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review. 📝 SummarySummary by CodeRabbit
WalkthroughThe offloader now calculates circular prefetch targets through ChangesPrefetch slot ownership
Estimated code review effort: 3 (Moderate) | ~15–30 minutes Merge Risk: ⚪ Minimal · up to This fixes prefetch target selection for non-divisible module rings while retaining circular prefetch behavior. The targeted coverage validates the changed target and slot-ownership behavior, with no remaining merge-blocking risk identified. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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/ci run |
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✅ Triggered Buildkite CI #87224 for commit |
…fload-slot-ownership
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/ci retry |
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✅ Triggered Buildkite CI #87346 for commit |
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/ci run |
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✅ Triggered Buildkite CI #87444 for commit |
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Hi @ZJY0516, thank you for approving this PR. All required CI checks are now green, including AMD MI300, NVIDIA H200, and Ascend NPU, and the PR is currently mergeable and clean. When you have a chance, could you please help merge it, or let me know if anything else is needed? Thanks! |
…llm-project#54975) Signed-off-by: Big2Wheel <1404207590@qq.com> Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com> Signed-off-by: Jyotirmoy Roy <jyotirmoyroy649@gmail.com>
3 participants
Purpose
Fix prefetch static-buffer corruption when the number of offloaded modules is not divisible by
prefetch_step.Static buffers are assigned by
module_index % prefetch_step, while the refill target was selected with(index + prefetch_step) % module_count. For a non-divisible shared-slot ring, wrapping can make the target belong to a different slot. That copy can overwrite a buffer still needed by an unexecuted module.For example, with three offloaded modules and
prefetch_step=2, modules 0 and 2 share slot 0 while module 1 owns slot 1. After module 1 executes, the old target is module 0, which overwrites slot 0 before module 2 executes.This change keeps the existing ahead-by-step target when it preserves slot ownership. On a cross-slot wrap, it instead advances within the chain of modules sharing the released slot. Divisible rings,
prefetch_step == 1, and non-shared slots preserve their existing behavior.Related Ascend runtime report: vllm-project/vllm-ascend#10932.
Relationship to #51710
After implementing and validating this focused fix, I found that the broader draft #51710 independently introduces a runtime controller with the same slot-local scheduling rule. This PR isolates only the correctness fix and regression coverage so it can be reviewed and merged independently of that larger offloader redesign. If this lands first, #51710 can rebase and drop the overlapping scheduling change.
Test Plan
Manual NPU comparison using Qwen3-0.6B on one Ascend 910B3:
prefetchbackendoffload_group_size=8offload_num_in_group=1offload_prefetch_step=2Test Result
6 passed.2 files already formatted).git diff --check: passed.0.209870383143425.0.000576317310333252.0.0.0.0.The NPU runtime validation used vLLM Ascend main
ff02be1e1ffc87d4b8135bca99a93f7d283067c9with its verified vLLM commitba07e4a48fc951300d97eb506217dd530583dea3. Upstream #53120 subsequently changed offload module discovery but retained the static-buffer slot assignment and refill formulas involved here. The focused unit, Ruff, and diff checks were rerun after rebasing the fix onto vLLM main2a4e3cc3dbddf4f44d69864209361f1e2a70c79a. The submission was then rebased without conflict ontoc6bca6e58540817bd6f192ae615dfa108cec1152; the offloader source and tests did not change between those last two revisions.AI assistance
AI assistance was used for code investigation, test orchestration, and drafting. Every changed line was reviewed by the submitter, and the reported tests and NPU measurements were executed on the stated environment.