[BugFix] Fix AssertionError: DCP not support reorder_batch_threshold > 1 now. #28751
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LucasWilkinson merged 1 commit intovllm-project:mainfrom Nov 15, 2025
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Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
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This pull request addresses an AssertionError related to reorder_batch_threshold in Decode Context Parallelism (DCP) mode by removing the problematic assertion from GPUModelRunner. Your reasoning that this check is brittle due to its reliance on a global environment variable (VLLM_ATTENTION_BACKEND) is correct. The responsibility for advertising backend capabilities should indeed lie with the backends themselves, and this change aligns with that principle. The logic within each AttentionMetadataBuilder appears to be the more robust place for such enforcement. This removal simplifies the code, improves modularity, and resolves the issue of false positive assertion failures. The change is approved.
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… > 1 now.` (vllm-project#28751) Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com> Signed-off-by: ym820 <yikai.mao@outlook.com>
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… > 1 now.` (vllm-project#28751) Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com> Signed-off-by: George D. Torres <gdavtor@gmail.com>
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… > 1 now.` (vllm-project#28751) Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
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… > 1 now.` (vllm-project#28751) Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>
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Fix
AssertionError: DCP not support reorder_batch_threshold > 1 now.caused by #27363Simply removing the assert; this assert has resulted in more false positives than true positives causing unnecessary thrash. The GPU model runner should not be responsible for tracking support of attention backends and ensuring they are advertising correct reorder batch thresholds; this would be better enforced via something like: #28750