[Misc] LoRA + Chunked Prefill

[aurickq]

Make LoRA work with chunked prefill, taking the same approach as #4994 but updated to latest code.

Also needed to modify the request sorting by the scheduler so prefill sequences always precede decoding sequences.

FIX #xxxx (link existing issues this PR will resolve)

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[NickLucche]

I believe putting all prefill requests first will break the Prefill/Decode ratio assumption as introduced here https://arxiv.org/abs/2308.16369, favoring memory-bound operations ends up in decreased throughput.

I am afraid I can't gather a lot of context from this PR, why is it needed to put prefills first here (converging to the default non-chunked scheduler policy)?

[aurickq]

I believe putting all prefill requests first will break the Prefill/Decode ratio assumption as introduced here https://arxiv.org/abs/2308.16369, favoring memory-bound operations ends up in decreased throughput.

I am afraid I can't gather a lot of context from this PR, why is it needed to put prefills first here (converging to the default non-chunked scheduler policy)?

My top-level comment was a bit ambiguous. The sorting is applied to the sequences within each batch, not in the scheduling queue, so it should not affect the ability to batch together prefill and decode sequences.

[rkooo567]

nit comments!

[mces89]

Hi, Can I ask when this pr can be merged so we can use this lora+chunked_prefill as soon as possible.

[kouroshHakha]

Hi @aurickq , awesome that you are working on this. Do you have an estimate on when this will be pushed over to finish line? Is this waiting on review or is there more blockers?

[aurickq]

@mces89 @kouroshHakha I rebased and all the tests are passing, just waiting for someone to merge it now. Perhaps @rkooo567 @simon-mo ?

[jeejeelee]

@aurickq Thanks for your contribution and patience