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[Kernel] Prototype integration of bytedance/flux kernels #5917

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[Kernel] Prototype integration of bytedance/flux kernels #5917

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tlrmchlsmth
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@tlrmchlsmth tlrmchlsmth commented Jun 27, 2024 •
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Summary

This is a rough prototype integration of the fused Gemm-ReduceScatter and AllGather-Gemm kernels from https://github.com/bytedance/flux.

The overall goal is to improve performance in the multi-GPU case by hiding the latency of collective communications by overlapping compute and data movement.

Instructions

To use this PR, first follow the instructions from the flux repo to build a wheel and then install it. You will also need to source the flux_env.sh file included in this PR. I had to manually set LD_LIBRARY_PATH to contain my venv's lib directory as well.

Performance

I am running the following to measure the latency of a request dominated by a large prefill:

python3 benchmarks/benchmark_latency.py --model meta-llama/Meta-Llama-3-8B-Instruct \
    --num-iters 100  --batch-size 1 --input-len 2048 --output-len 1 \
    --enforce-eager --tensor-parallel-size 4 --dtype float16

On 4 A100's:

This PR:

Avg latency: 0.04923512919805944 seconds
10% percentile latency: 0.048771245032548906 seconds
25% percentile latency: 0.04908173996955156 seconds
50% percentile latency: 0.04925268283113837 seconds
75% percentile latency: 0.04937761859036982 seconds
90% percentile latency: 0.04951343145221472 seconds
99% percentile latency: 0.050627540834248065 seconds

main:

Avg latency: 0.05624247697182 seconds
10% percentile latency: 0.05587919522076845 seconds
25% percentile latency: 0.05596787924878299 seconds
50% percentile latency: 0.05612784903496504 seconds
75% percentile latency: 0.05637543648481369 seconds
90% percentile latency: 0.05679564494639635 seconds
99% percentile latency: 0.05786421288736165 seconds
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@tlrmchlsmth tlrmchlsmth mentioned this pull request Jun 27, 2024
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@tlrmchlsmth tlrmchlsmth mentioned this pull request Jul 15, 2024
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@Rainlin007
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Tested in 13B model, it is more than 40% slower than the main branch. Is there a better optimization solution? Thanks

@tlrmchlsmth
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@Rainlin007 Could you share your test setup and numbers?

There are a couple of things that can be done to improve this PR's performance:

  1. The call to self.ag_gemm_op.reset_signals can be removed now that feat: fix tuning for the all-gather gemm && move the reset-signal() to the forward critical path bytedance/flux#19 has landed
  2. The argument fuse_reduction=True to the GemmRS kernel should be changed to False, but I am running into issues with that (see [BUG] Illegal memory access when fuse_reduction=False bytedance/flux#10)

After that, I think we'll see speedup on prefills and hopefully large batch size decodes.

@zheng-ningxin
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Tested in 13B model, it is more than 40% slower than the main branch. Is there a better optimization solution? Thanks

Which shape/model are you using? It’s possible that the default GEMM configuration performs poorly at this size. I can retune a GEMM configuration. Thank you.

@tlrmchlsmth
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@zheng-ningxin, @Rainlin007's comment was also posted on an earlier version of this PR, so @Rainlin007 you might want to try again now that I'm seeing speedup on my end.

@wenlei-bao
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wenlei-bao commented Aug 12, 2024 •
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Hey @tlrmchlsmth, is there any blocking issue to merge this PR (other than the format issue)? Please let us know if anything we could help to make this happen. :) cc @zheng-ningxin
Best.

@tlrmchlsmth
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Hey @wenlei-bao, one blocking issue is that this PR requires enforce_eager be true. That is, the last time I tried it, the Flux kernels don't support CUDA graphs. Do you know if this is still the case?

Beyond that, I need to do some benchmarking and develop some heuristics to decide when this optimization makes sense. The other thing worth mentioning is that ultimately, we don't want to rely on changing the model definition for the integration of the Flux kernels, but I think that the torch.compile rewrites are going slowly enough that it shouldn't block this PR from landing.

@Pinkypoopoo
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Pinkypoopoo commented Aug 13, 2024 via email

@wenlei-bao
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Hey @wenlei-bao, one blocking issue is that this PR requires enforce_eager be true. That is, the last time I tried it, the Flux kernels don't support CUDA graphs. Do you know if this is still the case?

Yes, we don't support/need CUDA graph yet.

Beyond that, I need to do some benchmarking and develop some heuristics to decide when this optimization makes sense.

Regarding the heuristics, you might also want to explore the scripts that in Flux tools/ folder for tuning different workloads (if apply), and incorporate different tiling choices for example to your heuristics (if to skip) or (in Flux tuning_config/ config files
if you want to config and apply Flux) as well to maximize the performance.

The other thing worth mentioning is that ultimately, we don't want to rely on changing the model definition for the integration of the Flux kernels, but I think that the torch.compile rewrites are going slowly enough that it shouldn't block this PR from landing.

Sounds great! Looking forward to it. @tlrmchlsmth

@tlrmchlsmth tlrmchlsmth mentioned this pull request Aug 26, 2024
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@tlrmchlsmth
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Abandoning this in favor of #9886!

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5 participants
@tlrmchlsmth @Rainlin007 @zheng-ningxin @wenlei-bao @Pinkypoopoo