Bi-weekly Journal: Contributions to vLLM

Summary

My bi-weekly journal for contributions to vllm.

July 24 – Aug 5

B200 Performance Optimization:

• Per-token-group quant CUDA kernel
  #21476 — 15× faster than the original Triton kernel (int8).
  #21867 — using __nv_fp8_e4m3, 10% faster for FP8.
  Works on all NVIDIA architectures, not only B200.
• NVFP4 optimization
  Bug fix for Compressed Tensor NVFP4: #21465
  Add FlashInfer MoE support for Compressed Tensor NVFP4: #21639 — ~15% E2E throughput.
• Other perf wins
  Non-contiguous support for FP8 quantization: #21961 — ~1% E2E throughput.
  Optimize reshape_and_cache_flash CUDA kernel: #22036 — 20–40% faster.

B200 New DeepGemm Integration:

• ✅ Done for this large scope! Special thanks to the help from Kaichao You and Chenggang Zhao

• Unit test used to debug: #21559 and log update: #22208

DBO Support:

• WIP: Collaborated with Sage and Lucas — exciting new scope.

Other Contributions:

• Several code-refactoring PRs merged:
  #21631, #21775, #21787
• Reviewed 10+ PRs.

July 9 – July 23

B200 Performance Optimization:

• Per-token-group quant CUDA kernel for FP8:
  #21083 — ~6% E2E improvement; works on all NVIDIA architectures.
• WIP at the time: per-token-group quant CUDA kernel for int8 (later landed as #21476).
• NVFP4 optimization:
  Bug fix for Compressed Tensor NVFP4 (ready to review then): #21465

B200 New DeepGemm Integration:

• Merged support for breaking DeepGEMM update on B200: #20087
  Upstream DeepGEMM PR: deepseek-ai/DeepGEMM #112
• Follow-up optimizations (all merged):
  DeepEP low-latency bugfix: #20833
  ~15% E2E perf improvement: #20841
  Breaking change fix: #21187
  CUDA init error fix due to DeepGemm: #21312

CI Bug Fixes:

• Found and fixed quickly: #20782, #20845

Other Contributions:

• Code-refactoring PRs merged: #20770, #20774, and others
• Reviewed 10+ PRs.

June 23 – July 8

B200 Performance Optimization:

• Quant vectorization utils optimization: #20331
  +3% E2E for CUDA quant kernels; reusable for FP8 quant, reshape_and_cache_flash, etc.

B200 New DeepGemm Integration:

• WIP then: support new breaking DeepGEMM for B200: #20087
  ~40% perf improvement for the GEMM kernel at specific batch sizes.
  Special thanks to Michael Goin and Varun Sundar Rabindranath.

B200 DeepEP & PPLX Validation:

• Bug fix: #20094 — validation done.

Severe CI Bug — Fixed:

• Issue raised (blocker in main for ~1 month): #20138
  Fix in two days: #20204

Other Contributions:

• Refactoring PRs merged: #20187, #20269, #20334, plus more
• Reviewed 10+ PRs.

June 9 – June 20

B200 Performance Optimization:

• align_moe_block_size kernel optimization: #19572 — ~6% E2E throughput.
• Benchmark script refactor for GEMM: #19627 — made future quant benchmarking easier.

B200 DeepGemm Integration:

• Initial integration: #19820 — ~40% GEMM perf improvement.
  Thanks to Robert Shaw!

B200 DeepEP Integration:

• Env setup & initial exploration.

Other Contributions:

• Helped review several PRs.

June 2 – June 7

B200 Performance Optimization:

• Int8 quant kernel optimization: #19233 — ~10% E2E throughput on B200.
  Thanks to Michael Goin’s guidance!
  My first vLLM PR!

Other Contributions:

• Raised issues and reviewed several PRs.