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+# Night shift — 2026-09-28
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+
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+## MiMo long-context cliff: vLLM A/B lane (the main event)
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+
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+Background: sglang 4x decode falls to 30% of d0 at 256K (77.6 → 23.5 t/s
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+slope sweep); GA layers' BF16 KV + kernel inefficiency. Operator asked for
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+the vLLM mirror (`mimo26-flash-mopd-4x-vllm`), modeled on lil-catalog.
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+
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+### The four r39 walls (19:0x–19:1x)
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+Four boots, four distinct failures — all in the fork's MiMo-unqualified gap:
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+EAGLE3 hook vs the Omni wrapper (patched), b12x rejecting the draft's
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+non-causal attention (triton workaround), `ModelOptMxFp8LinearMethod`
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+hard-import (patched), then fatal: KV-layout validator refuses MiMo's mixed
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+page sizes (SWA-128 + GA) because b12x declares LBNHC only. Spec written as
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+PARKED: `specs/bugs/BUG-2026-09-28-vllm-mimo-dflash-parked.md`.
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+
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+### Resolved by the ecosystem the same evening
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+- `local-inference-lab/vllm@dev/karmic-kraken` (eugr b12x nightly source)
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+ merged the MiMo series 09-22: aux-state loading, **block-outermost KV
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+ layouts for mixed page sizes**, **b12x non-causal**, eagle3 language-model
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+ unwrap, lazy mxfp8 guards. CI ships `eugr/spark-vllm-b12x:latest` arm64
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+ (v0.1.dev21546+g502d6cb5a) — pulled on dgx2, save/load-fabric'd to all
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+ nodes (~25 GB each).
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+- madeby561/vllm rc4 (b12x MiMo, FP8 KV, adaptive verification) is
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+ **linux/amd64 only** — not runnable on GB10; its compose kept as intel.
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+- Lane booted clean on the nightly: KV pool 8.57M tok, DFlash graphs on
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+ B12X, API serving. Our wrapper image + 2 patches retired (upstream
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+ equivalents shipped).
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+
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+### Garble and its root cause (21:15–20:3x)
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+First serving = multilingual junk in the reasoning channel (spec on AND
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+spec off — same garbage). Bisection found `--load-format instanttensor`
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+mis-maps MiMo's split-GDN weight naming: the lab launcher always loads MiMo
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+via the **b12x loader** (`VLLM_PLUGINS=b12x_loader`), full Omni +
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+`--mm-encoder-tp-mode weights` (not `--language-model-only`), explicit bf16
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+KV. Switching the contract → clean English/Russian immediately. DFlash
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+re-enabled per the Pro-TP8 launcher config (adds `kv_cache_dtype:auto`).
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+
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+### Quality (harness v2.7.1.dev7 — same as today's sglang anchor)
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+`2026-09-28_203145_vllm-kk-nightly-dflash`: **168/184 (91/100)** — exact
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+parity with sglang's 168/184 (91/100) from earlier today.
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+
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+### Long-context slope (`~/.cache/sm121/bench/slope-28x-vllm`)
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+pp2048 tg128 c1, runs=2; sglang from `slope-28x`:
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+
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+| depth | sglang | vLLM |
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+|---|---|---|
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+| d0 | 77.6 | 51.1 |
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+| 8192 | 76.2 | 54.0 |
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+| 32768 | 57.8 | 53.6 |
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+| 131072 | 33.7 | 33.7 |
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+| 262144 | **23.5** | **37.8** |
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+
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+**The cliff is flattened** (256K/d0: 0.30 → 0.74) — exactly what the
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+split-KV/verify line promised — at the cost of −34% d0 decode. If d0 decode
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+is improved (acceptance, b12x decode tuning), vLLM outright wins at long
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+context. Next dials: spec acceptance stats, GMU raise (nightly boots with
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+plenty of KV headroom), and whether `--max-num-scheduled-tokens` deserves
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+the 2048 the lab uses for interactive lanes.
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+
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+### Ops notes
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+- `sm121 serve` occupancy guard caught the crash-looped vLLM lane once;
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+ `sm121 stop --recipe` + rerun handled it.
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+- Bench/recipe churn today all pushed (see `git log` 2026-09-28).
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+- sglang 4x can be restored in ~2 min if the operator wants a fallback.
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