Speed on M5 Ultra: MLX 8-bit 69 tok/s, llama.cpp Q8_0 61, DSpark draft x1.3

#30
by tristanbes - opened

Speed numbers for the 12B on a Mac Studio M5 Ultra (256 GB), in case they help people pick a runtime. The README has M5 Max figures; on the Ultra the order flips and MLX comes out ahead of llama.cpp.

Runtime File Decode tok/s (median) Prefill tok/s (median) Peak memory
MLX 8-bit (mlx-lm 0.32.2) converted from model.safetensors with the README command (-q --q-bits 8 --q-group-size 64) 69.3 EN / 69.1 ZH 1,627 13.0 GB
llama.cpp Q8_0, Metal (0.7.0, build 11669) humanizer-12b-Q8_0.gguf, sha256 checked 61.0 EN / 61.0 ZH 1,333
MLX 4-bit target + Draftfit DSpark draft mlx-community/humanizer-12b-OptiQ-4bit @ e0e2552, runner settings from the draft card 92.6 (vs 71.4 target alone, Γ—1.30)

How it was measured

  • 5 drafts (email, blog, report, essay, Chinese email; 50–80 words each), 3 runs each, medians. Rewrites were 60–105 tokens, so these are short-output numbers.
  • MLX 8-bit and llama.cpp: exact prompt from prompt_format.json, temperature 1.0, top-p 0.95, top-k 0, min-p 0, repeat penalty 1.0, stop on EOS only. llama-server with -ngl 99 -c 8192 -fa on, cache_prompt: false.
  • DSpark: the draft card's setup (mlx 0.32.0, mlx-lm 0.31.3, patched mlx-dspark @ 4143092, FP32 target, 4-bit draft, greedy, draft cap 3, no lookup), up to 256 tokens. 15 of 15 outputs matched the target-only tokens exactly. Mean accepted length 2.4–2.9 per round; the Chinese draft gained least (Γ—1.21; the report gained most, Γ—1.51).
  • Machine otherwise idle, on AC power, no thermal warnings. Served through oMLX the 8-bit model gives about 61 tok/s end to end, HTTP included.

Takeaways for Apple silicon owners

  • On an M5 Ultra, MLX 8-bit is about 14% faster than llama.cpp Q8_0 at decode and about 22% faster at prefill.
  • The DSpark draft reproduces on the Ultra: about Γ—1.3 with identical output (the card reports +43% on an M5 Pro).

Thanks for the model and the careful docs, they made this easy to reproduce.

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