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[BugFix] Fix cascade attention - RuntimeError: scheduler_metadata must have shape (metadata_size) #17283

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Apr 28, 2025
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[BugFix] Fix cascade attention - RuntimeError: scheduler_metadata must have shape (metadata_size) #17283

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2 changes: 1 addition & 1 deletion vllm/v1/attention/backends/flash_attn.py
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Original file line number Diff line number Diff line change
Expand Up @@ -372,7 +372,7 @@ def schedule(batch_size, cu_query_lens, max_query_len, seqlens,
suffix_kv_lens = torch.from_numpy(suffix_kv_lens).to(
self.runner.device)
prefix_scheduler_metadata = schedule(
batch_size=num_reqs,
batch_size=1,
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@tlrmchlsmth tlrmchlsmth Apr 28, 2025

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Could you explain what was going on here a bit more?

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@LucasWilkinson LucasWilkinson Apr 28, 2025

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The prefix part of cascade attention is run as a single request (since its shared), this was a copy paste bug with the scheduling code

cu_query_lens=cu_prefix_query_lens,
max_query_len=num_actual_tokens,
seqlens=prefix_kv_lens,
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