[Kernel] sliding window support in paged_attention_v1/v2 kernels#4768
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mmoskal wants to merge 2 commits intovllm-project:mainfrom
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[Kernel] sliding window support in paged_attention_v1/v2 kernels#4768mmoskal wants to merge 2 commits intovllm-project:mainfrom
mmoskal wants to merge 2 commits intovllm-project:mainfrom
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cc @zhuohan123 (great timing!) |
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btw, we need to make sure this can be compatible with this PR #4681, that we plan to merge soon.. I think this can make things much cleaner |
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- Enables Sliding Window Attention (SWA) for the CPU backend. - Enables models with hybrid local-global attention (i.e., those with multiple KV cache groups) for the CPU backend. - Fixes a bug in `TorchSDPAMetadataBuilderV1` where `query_start_loc_cpu` was updated in-place despite being shared between multiple KV cache groups. - Adds a unit test for the decode phase in the CPU attention backend. - Adds reference implementations used to test paged attention to a common utils module and reuses it for the decode attention CPU test. SWA is enabled by truncating full blocks/pages that are outside the window (similar to vllm-project#23010). Hence, the implementation is block-granular and may attend to at most (block_size - 1) extra tokens; this did not affect the accuracy tests I ran. This is the best we can do with the current paged-attention API/implementation, which does not support SWA natively See: vllm-project#4768 for context and the attempt to enable native SWA support in paged_attn. Signed-off-by: Fadi Arafeh <fadi.arafeh@arm.com>
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The paged attention (v1 and v2) decode kernel does not support sliding window natively - the way it works now it just takes all the blocks passed in (up to seq_len). With v1 manager, the sliding window uses blocks in a "ring buffer" fashion, so this is not a problem. With the new block manager (see #4545) we need potentially to start attention computation in the middle of a block, otherwise we pay attention to a few tokens too many. It doesn't seem to affect this test though.
Related: #3385
This is just a rough draft - didn't even try to compile.
@cadedaniel is there another issue for this already?
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