[FEAT] Add support for AITER bpreshuffle block scale gemm

[tjtanaavllm]

Purpose

This PR add the use of aiter.gemm_a8w8_blockscale_bpreshuffle if shuffle is enabled.

It also remove the direct_register_custom_op overhead from aiter.gemm_a8w8_blockscale

aiter.gemm_a8w8_blockscale_bpreshuffle is used if and only if use_swizzle is True.

How to Tune

• https://github.com/ROCm/aiter/tree/main/csrc/ck_gemm_a8w8_blockscale_bpreshuffle

• https://github.com/ROCm/aiter/tree/main/csrc/ck_gemm_a8w8_blockscale

Alternative guide: https://github.com/EmbeddedLLM/vllmtests/tree/main/kernels/blockscalegemm

Test Plan

Evaluate the lm_eval score of Qwen/Qwen3-235B-A22B-Instruct-2507-FP8 before and after.

Evaluate the benchmark performance.

Test Result

lm_eval score

• Baseline

local-completions (model=Qwen/Qwen3-235B-A22B-Instruct-2507-FP8,base_url=http://127.0.0.1:6789/v1/completions), gen_kwargs: (None), limit: None, num_fewshot: None, batch_size: 100
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.8992|±  |0.0083|
|     |       |strict-match    |     5|exact_match|↑  |0.8946|±  |0.0085|

• After

local-completions (model=Qwen/Qwen3-235B-A22B-Instruct-2507-FP8,base_url=http://127.0.0.1:6789/v1/completions), gen_kwargs: (None), limit: None, num_fewshot: None, batch_size: 100
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     5|exact_match|↑  |0.9075|±  |0.0080|
|     |       |strict-match    |     5|exact_match|↑  |0.8976|±  |0.0083|

Performance

There are a few cases being evaluated

• Before removing vLLM’s direct_register_custom_op overhead
• Before removing vLLM’s direct_register_custom_op overhead (Tuned block scaled gemm)
• After removing vLLM’s direct_register_custom_op overhead (Tuned block scaled gemm)
• Using tuned bpreshuffle block scaled gemm instead of tuned block scaled gemm

Metric	Before Optimization	Before (Tuned Block)	After (Tuned Block)	Tuned BPreshuffle	Best Improvement
Throughput Metrics
Request throughput (req/s)	1.01	1.04	1.05	1.07	+5.9%
Output token throughput (tok/s)	979.19	1006.80	1017.31	1032.85	+5.5%
Total token throughput (tok/s)	4008.30	4125.60	4170.56	4232.04	+5.6%
Latency Metrics
Benchmark duration (s)	316.54	307.44	304.08	299.71	-5.3%
Mean TTFT (ms)	2342.34	2071.60	2258.43	2168.61	-11.6%
Median TTFT (ms)	2567.93	1733.94	2389.88	2310.13	-32.5%
P99 TTFT (ms)	7618.99	7087.36	7044.93	7102.27	-7.5%
Mean TPOT (ms)	32.30	33.76	30.98	32.20	-4.1%
Median TPOT (ms)	29.74	29.26	28.48	28.13	-5.4%
P99 TPOT (ms)	32.16	31.51	31.03	32.56	-3.5%
Mean ITL (ms)	29.57	28.93	28.42	28.06	-5.1%
Median ITL (ms)	21.53	21.31	21.10	20.48	-4.9%
P99 ITL (ms)	392.15	395.10	389.15	368.55	-6.0%

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