[Speculative decoding] [Multi-Step] decouple should_modify_greedy_probs_inplace #6971
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Will take a look tomorrow. |
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LGTM.
- Can we add a test for this? e.g. something that runs
include_gpu_probs_tensorbut without modified greedy probs, and we verify that the gpu probs tensor is there but the greedy probs are not modified. - The modification of greedy probs should not incur a CPU sync 😄 . I'll take a look at that.
| (self.scorer_worker.model_runner.model.sampler. | ||
| should_modify_greedy_probs_inplace) = True |
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Can we put this behind an interface so refactors to the worker / model / sampler do spread everywhere?
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Not sure if there is a clean way to do this, as the line above sets include_gpu_probs_tensor before this PR also change the decoupled (this PR) should_modify_greedy_probs_inplace. Seems the scorer worker is passed around as WorkerBase so would need to add change that class which is not ideal. Am I missing something?
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Oh right.. sorry I must have misread.
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By the way, what model is running in the profile ? pretty surprised by any CPU sync causing 17ms of overhead when the sampler already does a CPU sync at the beginning |
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This is llama 8B on A10G, but the profile is with multi-step, which has removed all the other sources of CPU syncs (CPU prepare_input, GPU<>CPU transfer for sampled token, pythonization) |
| (self.scorer_worker.model_runner.model.sampler. | ||
| should_modify_greedy_probs_inplace) = True |
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Oh right.. sorry I must have misread.
| @@ -1067,6 +1067,10 @@ def org_vocab_size(self): | |||
| def include_gpu_probs_tensor(self): | |||
| return self.base_layer.include_gpu_probs_tensor | |||
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| @property | |||
| def should_modify_greedy_probs_inplace(self): | |||
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Confused why this is here, why does this layer need it?
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I'm not sure, I just greped for all the places that include_gpu_probs_tensor was used and added the change there to keep semantics identical. See the lines above.
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Just added test for the inplace modification, let me know if there's anything else. |
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…bs_inplace (vllm-project#6971) Signed-off-by: Alvant <[email protected]>
Preparation PR for multi step. Not a blocker, but will make MS PR smaller and improve perf.
Decouple
should_modify_greedy_probs_inplacefrominclude_gpu_probs_tensorso that multi-step can setinclude_gpu_probs_tensorwithout also settingshould_modify_greedy_probs_inplaceand incurring the overhead of the probs modification (causes a GPU<>CPU sync). Not a blocker for multi-step, but does add ~1ms of GPU bubble between each step on A10G, will be a much bigger slow down on H100.@cadedaniel This may be a perf bug for spec decode as well?
I also can't seem to get spec_decode tests to all consistently pass locally?Torch Profile with multi-step and without decoupling (
should_modify_greedy_probs_inplace == True)cc @WoosukKwon @zhuohan123 @Yard1 @comaniac @rkooo567
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