[tx] Left align generated tokens in decoding #933
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This pull request refactors the Key-Value cache handling to support per-sequence cache positions, which is a crucial change for enabling efficient left-aligned batch decoding. The changes are consistently applied across the Llama3 and Qwen3 model implementations, as well as the generator utilities. The core logic of using per-sequence positions for updating the KV cache and attention mask seems correct. I've found one minor issue with a duplicated line of code that should be removed. Otherwise, the changes look solid.
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| # Pad KV cache and attention mask to max_length | ||
| kv_cache = kv_cache.pad_to_length(max_length) |
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This comment and the following line are redundant. The kv_cache is already padded to max_length on line 159. These lines can be removed.
tanmaysachan
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Jan 25, 2026
This PR writes the new decoded token into the kv cache in such a way that the whole sequence is left aligned. This is needed so that the CUDNN attention NovaSky-AI#879 truly works without attention mask.
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This PR writes the new decoded token into the kv cache in such a way that the whole sequence is left aligned. This is needed so that the CUDNN attention #879 truly works without attention mask.