club-3090/docs/FAQ.md

FAQ

Common questions about club-3090. If your question isn't here, open a GitHub Discussion — most things end up in this doc eventually.

Hardware

Can I use a 4090 instead of a 3090?

Yes — 4090 (Ada, sm_89) is strictly better than 3090 (Ampere, sm_86) for everything we ship. Slightly different kernel paths but no patches needed. Caveats: vLLM Genesis patches are tested on Ampere; tools should still work but TPS scaling is untested. Open an issue with numbers if you bench it.

Can I use a 5090?

Should work for vLLM (Blackwell adds new kernels but back-compat). The Marlin pad-sub-tile-n fork we mount targets Ampere edge cases — on Blackwell you can probably drop the /opt/ai/vllm-src/ mount. Not validated yet. We'd love numbers from a 5090 rig — use the Numbers from your rig issue template.

Do I need NVLink?

No. Our dual-card configs use PCIe-only, no NVLink. Custom all-reduce is disabled in the composes. NVLink would help dual-card TPS but it's not required, and the user has explicitly declined NVLink bridges as a default — adding the dependency would exclude most consumer rigs.

Does this work on AMD / Intel / Apple Silicon?

vLLM: NVIDIA-only (CUDA). llama.cpp: yes — pick the right Docker image (ghcr.io/ggml-org/llama.cpp:server-rocm for AMD, :server for CPU-only, or build from source for Apple Silicon). Update the image: line in the compose. The flags (--ngl, -fa on, --cache-type-k q4_0) work identically across backends.

Does this work on Windows / WSL2?

WSL2: yes, both engines. Make sure GPU passthrough is set up (nvidia-smi works inside WSL). Native Windows: vLLM doesn't support it; llama.cpp does — but use a native llama.cpp build, not Docker.

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Engine choice

Why ship both vLLM and llama.cpp?

Different trades. vLLM is faster (51-89 TPS depending on config) and has full feature support (vision · tools · MTP spec-decode · streaming · reasoning). As of 2026-04-30 PM, Cliff 1 (the 25K-token tool-prefill OOM) is closed on every shipped vLLM single-card variant via Genesis PN8 on the FP8 path and PN12 anchor sidecar on the TQ3 paths. The remaining caveat is Cliff 2 — single prompts above 50-60K still OOM in DeltaNet GDN forward, and that's a different memory class with no upstream fix yet. llama.cpp is slower (~21 TPS) but passes every stress test cleanly at full 262K context with vision and tools — including the big single prompts that vLLM single-card can't yet handle. See the launch frame: vLLM dual = max throughput, llama.cpp single = max robustness.

Why not Ollama?

Ollama wraps llama.cpp with a different model registry and slightly easier UX. It's fine for chat. Two reasons we don't ship it:

1. Ollama doesn't expose all llama.cpp flags we need (--cache-type-k q4_0, --mmproj, --spec-type ngram-mod, custom --parallel).
2. Ollama's model registry doesn't have the exact Unsloth GGUF quants we ship (UD-Q3_K_XL). You can run Ollama against an Unsloth GGUF manually, but at that point you've reimplemented our llama.cpp compose with a different wrapper.

Why not LM Studio?

LM Studio is GUI-driven and great for hobbyist use. We ship CLI/Docker because:

• Reproducibility — pinned image SHAs + Genesis commit make exact bench runs across machines possible
• Headless deployment — homelab racks, dev backends
• Tool-call extraction across both engines on this exact model is non-trivial; LM Studio's defaults haven't been validated

Use LM Studio if you prefer a GUI and don't need the engineering. Use this repo if you want a tested config that another club-3090 user can match exactly.

Why MTP and not EAGLE?

We tried EAGLE — it's blocked on Qwen3-Next (the family Qwen3.5/3.6 belong to) by DeltaNet hybrid attention's lack of KV rollback support in vLLM/SGLang. MTP works because it's a different protocol (multi-token prediction at draft-head level, not a separate draft model). See INTERNALS.md "Speculative decoding" for the full forensic chain. Re-test triggers: if vllm#39931 lands or DeltaNet rollback support arrives upstream, EAGLE becomes viable again.

Why not GGUF on vLLM for this model?

Multiple gates blocked. Qwen3.6-27B GGUF on vLLM hits a chain of "fixed but-not-quite" issues — multimodal config routing, ParallelLMHead skip, the Qwen35TensorProcessor._reverse_reorder_v_heads weight loader producing garbage output on the 27B layout (transformers PR #45283 only validated on 0.8B). Tracked in INTERNALS.md. Use llama.cpp for GGUF on this model.

Why AutoRound INT4 not GPTQ / AWQ?

AutoRound (Lorbus) gave us +9% TPS over AWQ on this model. GPTQ has a similar quality bar but the AWQ + DFlash path failed (pad-Marlin × aux-layer interaction). AutoRound + Genesis + MTP is the production-validated path. AWQ is documented as a fallback for users who can't use AutoRound.

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Performance

Why is single-card TPS lower than I expected?

Look at the TPS chart — single-card vLLM is 51-55 TPS narrative / 67-70 code at 48K, which beats most consumer-3090 numbers we've seen reported. If you're seeing materially lower, the most common causes are:

1. Power cap < 230 W (this rig benches at 230 W; 280 W gives ~+5%, 350 W ~+10%)
2. Wrong compose for your prompt shape (use the docker-compose.yml 48K default for chat — don't pick long-vision.yml if you don't need 198K)
3. Genesis tree drift — git pull origin main between bench runs can change AL by ±15%. We pin to commit bf667c7 for this reason.

My TPS dropped after switching to 198K context. Why?

It shouldn't, much — we measured 50.93 TPS narr at 192K vs 50.53 at 32K (within variance) on long-vision.yml pre-fix; the new 198K + 0.98 config is in the same range. If it dropped a lot, you're probably actually decoding into a long ctx (not just having KV pool reserved). Loaded-context decode is 2-4× cold short-prompt decode on any LLM. The TPS chart number is short-prompt cold; loaded numbers are in BENCHMARKS.md.

What's a "prefill cliff"?

VRAM-related OOM during prompt processing on single-card vLLM. Two cliffs documented:

• Cliff 1 — historical: FFN intermediate buffer (SiluAndMul output, 138 MiB at max_num_batched_tokens=4128 × intermediate_size=17408 × 2 bytes) fresh-allocated per layer. Plus a related FA2 softmax_lse cap-leak (Dao-AILab/flash-attention#1011). Closed on every shipped vLLM single-card variant as of 2026-04-30 PM: tools-text.yml via Genesis PN8 (frees ~900 MiB on FP8 path); long-vision.yml and long-text.yml via the PN12 anchor sidecar (PR #13 to Sandermage's repo) plus a local P104 FA softmax_lse clamp. Full diagnostic: docs/CLIFFS.md.
• Cliff 2 — DeltaNet GDN forward OOM at ~50-60K single-prompt regardless of mem-util. Different memory class, lives in fla.ops upstream, no file-replacement patch yet. Tracked in UPSTREAM.md. Mitigation: dual-card TP=2 (verified at 237K) or llama.cpp single-card (262K, different engine).

For the full deep dive — empirical bisection, root-cause walk-through, who-can-fix-it landscape, and what we could do at any difficulty level — see docs/CLIFFS.md.

vllm#40914 keeps coming up — what is it?

Sandermage's K+1 verify routing PR for vLLM. When it lands, the spec-verify cost we're paying on Ampere SM 8.6 (~22 TPS narrative regression vs pre-bug substrate) closes. Our default on 0.20.1rc1.dev16+g7a1eb8ac2 + Genesis v7.65 dev tip will jump from ~50 narr to ~70 narr, matching what ampersandru measures on the older dev21 + v7.13 cascade-prone substrate. We track it in INTERNALS.md "Upstream tracker".

What's PN8?

A Genesis patch (GENESIS_ENABLE_PN8_MTP_DRAFT_ONLINE_QUANT=1) added in v7.62.x — backport of vllm#40849 that makes the MTP draft head inherit the target model's online-quant config. We measured ~800-900 MiB freed on the FP8+MTP single-card path (tools-text.yml), which closes Cliff 1 there. No-op on TQ3 paths. Enabled by default in tools-text.yml since 2026-04-29; opt-in elsewhere via the env var if you want to test.

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Setup

bash scripts/setup.sh qwen3.6-27b is downloading 20+ GB. Where does it go?

<repo>/models-cache/ by default. Override with MODEL_DIR=/path/to/your/scratch bash scripts/setup.sh qwen3.6-27b. See .env.example for all env vars.

My GPU isn't card 0 — how do I change it?

CUDA_VISIBLE_DEVICES=2 bash scripts/launch.sh --variant vllm/default (substitute your card index). For dual-card, pass two: CUDA_VISIBLE_DEVICES=2,3. The compose files inherit env from your shell.

Container fails to start: "Free memory ... is less than desired GPU memory utilization"

Looks like:

ValueError: Free memory on device cuda:0 (22.76/24.0 GiB) on startup
is less than desired GPU memory utilization (0.97, 23.28 GiB).

vLLM's startup check reserves mem-util × total VRAM of currently-free VRAM before booting. If something else on the GPU is holding memory (X11 / Wayland compositor, leftover container, Python process, browser GPU acceleration), the check fails. Most common on tools-text.yml (0.97) and the long-* variants (0.98 / 0.985).

Two fixes:

1. Free the VRAM (preferred). nvidia-smi shows what's holding it. Common: log out of GUI, stop a leftover container (docker rm -f $(docker ps -aq --filter "name=vllm-")), or kill orphaned python processes.
2. Lower mem-util in the compose. e.g. on tools-text.yml: drop --gpu-memory-utilization 0.97 to 0.94 and reduce --max-model-len proportionally (75K → ~70K). Loses ~6K context but works on any rig.

The 0.97 / 0.98 / 0.985 defaults assume a headless rig with ≥23.3 GiB consistently free. If you're running a desktop session on the same card, 0.92–0.94 is the safer ceiling.

Can I run multiple variants at once on the same machine?

You'd need different ports per variant. Set PORT=9876 in .env (or pass inline: PORT=9876 bash scripts/switch.sh vllm/default) — every shipped compose now reads ${PORT} for the host-side port mapping. Watch VRAM — two configs simultaneously typically don't fit on 24 GB.

Will this work behind Open WebUI?

Yes. Add a connection in Open WebUI's Settings → Connections → OpenAI: base URL http://localhost:8020/v1, any non-empty API key, model qwen3.6-27b-autoround. See docs/EXAMPLES.md.

Will this work with VS Code GitHub Copilot LLM Gateway?

Yes, but you need a compose with ≥48K context — Copilot's LLM Gateway sends ~20K tokens of tool-schema preamble (50+ VS Code tools enumerated in a structured-outputs JSON schema) on every request, which alone consumes most of a small context budget. Use tools-text.yml (75K + fp8 + PN8 enabled — Cliff 1 closed):

bash scripts/switch.sh vllm/tools-text

There's a second wrinkle: Copilot's LLM Gateway sometimes sends very low max_tokens (e.g. 64) on probe-style requests. With tool_choice: required (which Copilot enforces via minItems: 1 on its structured-outputs schema), the model must emit a tool-call JSON that wraps a real argument like a file path — and 64 tokens isn't enough to fit {"name": "read_file", "parameters": {"filePath": "/long/abs/path"}}. The truncated JSON arrives at the gateway as "empty response." If you see this pattern, it's a client-side limit, not the server. Other OpenAI-compat clients (Cline / Continue.dev / Cursor) tend to send realistic max_tokens by default and don't hit this.

Server-side fix landed 2026-04-29: the Genesis P68/P69 long-context tool-adherence patches were silently overriding tool_choice: auto → required and injecting "must use a tool" reminders whenever prompt > 8000 chars. That made greetings + clarifying questions stall on every IDE-agent setup (Cline, Cursor, OpenCode, and Copilot Gateway combined). We disabled both in tools-text.yml. Behavior now: greeting → plain-text reply ("Hello! How can I help you today?"); tool request → clean read_file({"path": "..."}) call. P64 and PN8 stay enabled (real targeted bugfixes, no user-intent override).

Background + bisection: club-3090 #2.

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Community / contribution

Can I add my benchmark numbers from a different rig?

Please do — open an issue using the Numbers from your rig template. We collect cross-rig data points in BENCHMARKS for community signal.

Found a bug — what should I include?

The bug report template asks for the data we always need: docker logs --tail 100, verify-full.sh output, nvidia-smi, your compose variant, and the repo commit. Skipping these means the first reply will just ask for them, costing you a round-trip.

How do I bump Genesis to a newer commit?

GENESIS_PIN=<new-commit-sha> bash scripts/setup.sh qwen3.6-27b and re-run bash scripts/verify-full.sh to confirm tools still work. Don't bump in production without re-running the verify suite — Genesis releases sometimes change spec-verify routing in ways that affect tool-call extraction.

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Troubleshooting

Quick recognition guide for common failure modes:

• Container dies at boot with GPTQ_MARLIN_MIN_THREAD_N (64) > out_features — dual-card vllm#40361 patch didn't apply. Confirm /opt/ai/vllm-src/ exists with the patched marlin kernel files.
• Container dies during DFlash boot — vllm#40334 dtype mismatch. Verify the compose has --dtype bfloat16.
• Tool calls return <tool_call> as plain text — Genesis didn't apply. Check Genesis Results: 27 applied in logs (boot-time).
• OOM during prefill at 60K+ tokens — single-card Cliff 2 (DeltaNet GDN forward). Switch to lower max-model-len, dual-card, or llama.cpp + q4_0 KV.
• OOM during prefill at 25K+ tool response — historically Cliff 1 on TQ3 paths. Closed since 2026-04-30 PM via PN12 anchor sidecar on long-vision.yml / long-text.yml. If you're hitting it, check your compose has the sidecar wired in (patch_pn12_ffn_pool_anchor.py in entrypoint).
• "Empty response" through VS Code Copilot LLM Gateway — Copilot sends ~20K tokens of tool schemas + sometimes uses max_tokens=64 which truncates tool-call JSON. Switch to tools-text.yml (75K) and check Copilot's max_tokens setting. See #2 for full debug-log analysis.
• Per-stream TPS lower than expected — re-run bench.sh with 3+ warmups + 5 measured runs first. Run-to-run variance is ~5%.

If none match, open an issue with docker logs <container> 2>&1 | tail -200 + nvidia-smi — see bug-report.yml template.

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See also

• README — top-level overview + quick start
• docs/SINGLE_CARD.md — 1× 3090 deployment menu
• docs/DUAL_CARD.md — 2× 3090 deployment menu
• models/qwen3.6-27b/README.md — model-specific reference
• models/qwen3.6-27b/INTERNALS.md — engineering deep dive
• docs/EXAMPLES.md — Python / TS / curl client snippets
• docs/HARDWARE.md — Ampere notes, NVLink, power caps
• docs/GLOSSARY.md — TPS / KV / MTP / TP / etc. plain-language definitions