Frank
0eda208705
Recording the 54-config matrix, the realistic-prompt correction (n_max=5 not 10), the ubatch findings (256 is the safe/fast point), and the premature-stop sampling-variance investigation.
87 lines
2.8 KiB
Markdown
87 lines
2.8 KiB
Markdown
# Qwen3.8-27B UD-Q8_K_XL Speculative-Decoding Matrix
|
|
|
|
This page records the speculative-decoding benchmark and the production
|
|
tuning for the unsloth Qwen3.8-27B `UD-Q8_K_XL` service on Dankclaw
|
|
(`frank-default-large`).
|
|
|
|
## Result (applied)
|
|
|
|
- Model: `Qwen3.8-27B-UD-Q8_K_XL.gguf` (29.29 GiB, bundled MTP).
|
|
- Spec: `draft-mtp`, `--spec-draft-n-max 5`, no `--spec-draft-p-min`.
|
|
- Batch 8192 / ubatch 256, parallel 2, ctx 524288 (262144 per slot).
|
|
- Realistic-prompt generation: ~13.3 t/s single, ~8 t/s per slot under
|
|
2 concurrent streams. No premature stop.
|
|
|
|
## How MTP works on Qwen3.8
|
|
|
|
The unsloth `UD-*` GGUFs keep the MTP (Multi-Token Prediction) head inside
|
|
the model file. llama.cpp b10411+ auto-detects it and creates the draft
|
|
context from the target model. Do not pass `--spec-draft-model`.
|
|
|
|
The stock llama.cpp build must be b10411 or newer. The 2026-08-14 rebuild
|
|
on Dankclaw is b10433 (`9b05354ec`) with `GGML_HIP` + `gfx1151` + Vulkan.
|
|
|
|
## Benchmark Method
|
|
|
|
The matrix ran 54 configurations: 3 spec types (`draft-mtp,ngram-mod`,
|
|
`draft-mtp`, `ngram-mod`) x `--spec-draft-n-max` 2..10 x
|
|
`--spec-draft-p-min` {off, 0.8}. Each config loaded `llama-server`,
|
|
then ran 3 generations. The tool is `scripts/spec-matrix-bench.sh`;
|
|
analysis is `scripts/analyze-spec-matrix.py`.
|
|
|
|
## Matrix Caveat: Benchmark Prompt
|
|
|
|
The matrix used a repetitive 1100-token prompt
|
|
(`scripts/bench_live.sh` style). MTP drafts that repeated sentence almost
|
|
perfectly, which inflated the numbers for long drafts. The matrix reported
|
|
`draft-mtp` n_max=10 at ~30 t/s. A realistic story prompt gave very
|
|
different results:
|
|
|
|
| n_max | median t/s (realistic) |
|
|
| ----- | ----------------------- |
|
|
| 4 | 12.5 |
|
|
| 5 | 13.3 (peak) |
|
|
| 6 | 10.6 |
|
|
| 7 | 10.1 |
|
|
| 10 | 8.6 |
|
|
| none (baseline) | 7.2 |
|
|
|
|
Long drafts collapse to ~18% acceptance on real writing. n_max=5 balances
|
|
acceptance against draft cost.
|
|
|
|
## Premature Stop Investigation
|
|
|
|
Two failure patterns appeared during early production tests:
|
|
|
|
1. Speed collapse. `ubatch >= 512` reduced MTP acceptance to ~25% and
|
|
generation to ~9 t/s. `ubatch 128` with `batch >= 2048` triggered a
|
|
premature instant-EOS under 2 concurrent slots. `ubatch 256` avoids
|
|
both: ~30 t/s single, concurrent-safe.
|
|
2. Apparent premature-EOS. The repetitive benchmark prompt with `temp 1.0`
|
|
sometimes stops after 1-2 tokens because the model legitimately emits an
|
|
EOS on a wall of repeated text. This is sampling variance, not a
|
|
corruption bug. Realistic prompts never stop early.
|
|
|
|
## Production Configuration
|
|
|
|
`scripts/frank-default-large.env`:
|
|
|
|
```ini
|
|
SPEC_TYPE=draft-mtp
|
|
SPEC_DRAFT_N_MAX=5
|
|
SPEC_DRAFT_P_MIN=
|
|
BATCH_SIZE=8192
|
|
UBATCH_SIZE=256
|
|
CTX_SIZE=524288
|
|
PARALLEL=2
|
|
```
|
|
|
|
Window: 524288 total / 2 = 262144 per slot, matching the pi
|
|
`models.json` contextWindow for `frank-default-large`.
|
|
|
|
## See Also
|
|
|
|
- [[frank-default-large-benchmark]]
|
|
- [[ling-3.0-flash-trial]]
|
|
- [[deployment]]
|