misc: Customize kv lens buffer size for sparse attention #1383
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Summary of Changes
Hello @Edenzzzz, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request enhances the flexibility of the sparse attention mechanism by making the size of its internal key-value (KV) lens buffers configurable. This change allows for better memory management and performance tuning for different sparse attention use cases, addressing a previous limitation where these buffer sizes were fixed.
Highlights
- Configurable KV Lens Buffer Size: I've introduced a new
kv_lens_buffer_sizeparameter to theBlockSparseAttentionWrapper's constructor inflashinfer/sparse.py. This parameter, defaulting to32768, allows users to customize the size of the internal buffers used for sparse attention. - Dynamic Buffer Allocation: The
_vector_sparse_indptr_bufferand_kv_lens_bufferwithin theBlockSparseAttentionWrappernow dynamically allocate their size based on the newkv_lens_buffer_sizeparameter, replacing previously hardcoded values.
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| kv_lens_buffer_size : int | ||
| The size of the kv lens buffer (num_kv_heads * MB), defaults to 32768. | ||
| """ |
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The description for kv_lens_buffer_size states the size is (num_kv_heads * MB), but for BlockSparseAttentionWrapper, the required size for _kv_lens_buffer is MB (number of block rows) and for _vector_sparse_indptr_buffer it's MB + 1. The (num_kv_heads * MB) seems to be from VariableBlockSparseAttentionWrapper and is misleading here.
Also, the parameter is used for both _kv_lens_buffer and _vector_sparse_indptr_buffer, so the docstring could be more precise by mentioning both.
| kv_lens_buffer_size : int | |
| The size of the kv lens buffer (num_kv_heads * MB), defaults to 32768. | |
| """ | |
| kv_lens_buffer_size : int | |
| The buffer size for KV lens and sparse indptr (>= MB). Defaults to 32768. |
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Can we allocate dynamically in the |
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It would be problematic if we want to support cuda graph later |
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Got it. Your PR works for me, thanks for your fix! |
📌 Description
🔍 Related Issues
Fixes #1367
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