[ Kernel ] Enable Dynamic Per Token fp8

[robertgshaw2-neuralmagic]

SUMMARY:

• turns on dynamic per token quantization for fp8
• enables fallback if cutlass kernels are not supported
• add test cases

RESULTS:

nm-testing/Meta-Llama-3-8B-Instruct-W8A8-FP8-Channelwise-compressed-tensors

• GSM with dynamic per token:

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value|   |Stderr|
|-----|------:|----------------|-----:|-----------|---|----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.753|±  |0.0136|
|     |       |strict-match    |     5|exact_match|↑  |0.756|±  |0.0136|

• GSM with dynamic per tensor:

|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value|   |Stderr|
|-----|------:|----------------|-----:|-----------|---|----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.748|±  |0.0137|
|     |       |strict-match    |     5|exact_match|↑  |0.747|±  |0.0138|

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[robertgshaw2-neuralmagic]

/ready

[mgoin]

Shouldn't use_per_token_if_dynamic be set by a scheme or something? I don't see why it should always be true for this case

[robertgshaw2-neuralmagic]

In what case would we not want to use dynamic per token?

[tlrmchlsmth]

@mgoin the hypothesis here is that dynamic per token is an overall win over dynamic per tensor when supported. Higher accuracy, but also easier to fuse RMSNorm + Quant, and fewer dependencies so better parallelization for the quantize kernels overall. Downside is more scales.

We'll need to benchmark, but IMO ok for this PR

[mgoin]

I assume there is a decent performance hit compared to produce/using per-tensor scale, is this not the case?

[tlrmchlsmth]

I wouldn't assume a decent performance hit -- the overheads from the CUTLASS epilogues are quite small (like 3%), and there are advantages to doing per-token when quantizing as well. We'll measure.

[tlrmchlsmth]

I changed my mind -- as I am implementing the per-token/per-channel wrapper for torch._scaled_mm, I think it would be nicer to grab this from a config somewhere

[robertgshaw2-neuralmagic]

I tried to pass this from the scheme. However, this became very hard because I needed to check if cutlass is supported in multiple places

I think that deciding this here is the right place

[robertgshaw2-neuralmagic]

DO NOT LAND UNTIL VARUNS PR GOES IN FIRST