feat: support non-contiguous (packed) input for prefill kernels #404
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yzh119
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🤖 I have created a release *beep* *boop* --- ## [0.1.2](v0.1.1...v0.1.2) (2024-07-29) ### Bugfix * Fix the sampling kernel bug for cu118 ([#386](#386), [#387](#387)) ([0cd499](0cd4994), [dc3f18](dc3f184)) ### Features * add llama 3.1 style rope ([#401](#401)) ([4c89dec](4c89dec)) * non-inplace rope operators ([#405](#405)) ([74ffba1](74ffba1)) * sliding window attention ([#406](#406)) ([28cffd3](28cffd3)) * support non-contiguous (packed) input for prefill kernels ([#404](#404)) ([68c3719](68c3719)) ### Performance Improvements * slight optimization on merge states ([#313](#313)) ([701c813](701c813)) --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). --------- Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com> Co-authored-by: Zihao Ye <expye@outlook.com>
yzh119
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Oct 25, 2024
## Motivation Previously, only ragged version of prefill kernel supported non-contiguous query tensor (#404). But with paged kv cache, you have to make query tensor contiguous. Libraries like vLLM or SGLang must make query tensor contiguous before calling flashinfer kernels ([vLLM call of flashinfer](https://github.com/vllm-project/vllm/blob/b7df53cd42f3eab007b4f287c151960858e949df/vllm/attention/backends/flashinfer.py#L839), [SGLang call of flashinfer](https://github.com/sgl-project/sglang/blob/87a7cfa080cec3f123618c1429b5f998bf5d99cb/python/sglang/srt/layers/attention/flashinfer_backend.py#L236)). This PR solves it, ensuring that prefill/decode kernels with paged kv cache support non-contiguous query tensor. ## Main Changes 1. Add strides of query tensor in `BatchPrefillPagedParams` and `BatchDecodeParams`. 2. Set stride parameters before calling those kernels. 3. Modify JIT compiling templates to support new kernel parameters. 4. Add some tests. The Python interfaces remain the same. Nothing changes except it accepts non-contiguous query tensors now! --------- Signed-off-by: LinHeLurking <LinHe.Lurking@gmail.com>
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This PR implements #311 , after this PR, we support packed qkv input without explictly convert make the input contiguous:
Before this PR, we need to make
q/k/vcontiguous before we launch the attention kernel, which incurs some overhead.I observe slight (<1%) performance degration after this PR for non-packed input, which is acceptable IMO.