Per-GPU specs and autotune math — single-GPU llama.cpp tier

Source of truth for the per-GPU JSON configs in this directory (3090.json, 4090.json, 5090.json, h200.json) and for the gpu-autotune.ts helper in packages/app-core/src/services/local-inference/.

Scope: one GPU per host. No tensor parallelism, no NVLink splits, no multi-tenant scheduling. The product target is "one conversation at a time on a single GPU box."

Inference engine: llama.cpp / llama-server (the buun-llama-cpp fork that ships the QJL + Polar KV quant kernels). This file does not cover vLLM / SGLang — those have different memory and parallelism models.

All expected_metrics in the JSON configs are extrapolated, not measured. The _provenance: "extrapolated" field marks that explicitly. A real benchmark on each card replaces these once a runner is wired.

Spec table

Card	Arch (CC)	VRAM	Mem-BW	FP16 TFLOPs	FP8 TFLOPs	FP4 TFLOPs	INT4 TFLOPs	Max ctx (rec.)	Max parallel	Target RTF (voice)
RTX 3090	Ampere sm_86	24 GiB GDDR6X	936 GB/s	71	—	—	284	65 536	4	0.55
RTX 4090	Ada Lovelace sm_89	24 GiB GDDR6X	1 008 GB/s	165	660 (E4M3/E5M2)	—	660	131 072	8	0.40
RTX 5090	Blackwell sm_120	32 GiB GDDR7	1 792 GB/s	209	838	1 676	838	262 144	12	0.30
H200 SXM	Hopper sm_90	141 GiB HBM3e	4 800 GB/s	989	1 979	—	1 979	1 048 576	16	0.20

RTF = real-time factor; lower is better. For voice streaming we need RTF < 1 for steady-state and < 0.5 to leave headroom for TTS + ASR.

Citations

• RTX 3090 — NVIDIA Ampere GA102 whitepaper (2020). 24 GB GDDR6X at 19.5 Gbps × 384-bit = 936 GB/s. No FP8 tensor cores. Compute capability sm_86. flash-attn 2 supported; flash-attn 3 is Hopper-only.
• RTX 4090 — NVIDIA Ada Lovelace AD102 whitepaper (2022). 24 GB GDDR6X at 21 Gbps × 384-bit = 1 008 GB/s. FP8 E4M3/E5M2 tensor cores (4th gen). Compute capability sm_89. flash-attn 2; flash-attn 3 kernels upstreamed but Hopper-tuned.
• RTX 5090 — NVIDIA Blackwell GB202 whitepaper / launch deck (2025). 32 GB GDDR7 at 28 Gbps × 512-bit = 1 792 GB/s. 5th-gen tensor cores with FP8 + FP4 (E2M1). Compute capability sm_120. llama.cpp sm_120 kernel coverage is incomplete in early Blackwell builds — buun-llama-cpp records this in CAPABILITIES.json; the runtime probes it before promising QJL/Polar.
• H200 SXM — NVIDIA H200 datasheet (2024). 141 GB HBM3e at 4.8 TB/s. FP8 transformer engine (4th gen). Compute capability sm_90. Flash-attn 3 first-class.

llama.cpp issues:

• Blackwell support tracking: https://github.com/ggml-org/llama.cpp/issues/11279
• KV cache quantization Q8/Q4: https://github.com/ggml-org/llama.cpp/pull/7527
• flash-attn-3 for Hopper: https://github.com/ggml-org/llama.cpp/pull/13306

Autotune math

Two budgets dominate every choice:

1. VRAM budget — model weights + per-slot KV must fit.
2. Memory bandwidth budget — steady-state decode throughput is (weights-per-token) / (mem-bw). RTF ≈ tokens-per-second-audio / tokens-per-second-decode.

KV-cache cost per token

Transformer KV cost: bytes/token = 2 × n_layers × n_kv_heads × head_dim × bytes_per_element (factor of 2 = K and V).

Eliza-1 bundles (Qwen3.5 / 3.6 base):

Bundle	n_layers	n_kv_heads	head_dim	FP16 KiB/tok	Q8K/Q4V KiB/tok	QJL+Polar KiB/tok
0.8B / 2B class	28	8	128	112	88	28
4B	36	8	128	144	113	36
9B	48	8	128	192	150	48
27B	62	8	128	248	194	62

Per-slot KV at recommended context

Bundle	Ctx	KV quant	KV per slot
2B	32k	Q8K/Q4V	32 768 × 88 KiB = 2.75 GiB
2B	32k	QJL+Polar	32 768 × 28 KiB = 0.88 GiB
9B	65k	QJL+Polar	65 536 × 48 KiB = 3.0 GiB
27B	32k	QJL+Polar	32 768 × 62 KiB = 2.0 GiB
27B	128k	QJL+Polar	131 072 × 62 KiB = 8.0 GiB
27B	256k	QJL+Polar	262 144 × 62 KiB = 16.0 GiB

Parallel slot derivation

VRAM available for KV ≈ vram - model_weights - reserved_headroom. Reserved headroom (driver + activations + drafter): 3 GiB on 24 GB cards, 4 GiB on 5090, 6 GiB on H200. See reservedHeadroomGb() in packages/shared/src/local-inference/gpu-profiles.ts.

RTX 3090 (24 GiB, no FP8) — uses Q8K / Q4V KV (Ampere has no q4_polar kernel on the Polar fork).

• 2B (1.5 GiB model): KV budget 19.5 GiB / 2.75 GiB-per-slot = 7 max parallel @ 32k. Config caps at 8 to leave OS-window headroom.
• 9B (5.4 GiB): KV budget 15.6 GiB / (65 536 × 150 KiB = 9.4 GiB-per-slot @ 64k) = 1 parallel @ 64k; at 32k it's 4.7 GiB-per-slot → 3 parallel. Config picks 4 with kvSpillToCpu opt-in at 64k.
• 27B (16.8 GiB): KV budget 4.2 GiB / 2 GiB-per-slot @ 32k = 2 parallel.

RTX 4090 (24 GiB, FP8) — QJL + Polar KV available.

• 2B: KV budget 19.5 GiB / 0.88 GiB-per-slot @ 32k = 16 parallel (we cap at 16 for practical session-count reasons).
• 9B: 18 GiB / 3 GiB-per-slot @ 64k = 6; spec picks 8 parallel @ 32k (slot KV = 1.5 GiB) for voice; 4 @ 64k for chat.
• 27B: 4.2 GiB / 2 GiB-per-slot @ 32k = 2 parallel.
• voice (omnivoice + small LLM): omnivoice runs on CPU/Metal in fused mode; KV is only the small text drafter. Cap 4 parallel at 8k for the voice loop.

RTX 5090 (32 GiB, FP8/FP4) — same KV math, 8 GiB more headroom.

• 2B: KV budget 27.5 GiB / 0.88 GiB = 31 → 24 parallel (we leave realistic session headroom).
• 9B: 26.6 GiB / 3 GiB @ 64k = 8 → 12 parallel @ 64k.
• 27B: 12 GiB / 2 GiB @ 32k = 6 → 6 parallel @ 32k; at 128k it's 8 GiB per slot → 1.5 → 1 parallel @ 128k.

H200 (141 GiB) — the marquee box.

• 27b: 8 GiB per slot @ 128k → 16 parallel (capped).
• 9b: ~0.45 GiB per slot @ 8k → 64 parallel.

Batch / ubatch derivation

• batch_size = logical batch fed to the prefill kernel per server tick. Doubles with VRAM (more headroom for activations) but caps at 4096 — beyond that, llama.cpp scheduler overhead eats the win.
• ubatch_size = physical micro-batch the GPU launches. Ada / Blackwell / Hopper want ≥ 512 to keep tensor cores saturated; Ampere is happiest at 256-512.

Card	batch	ubatch	Why
3090	2048	512	Ampere; mem-bw-bound past 512 ubatch
4090	2048	512	Same dies as 3090 family; FP8 helps prompt eval not decode
5090	4096	1024	More SMs + GDDR7 bw lets the bigger ubatch land
H200	4096	2048	HBM3e + sm_90 tensor cores; bigger ubatch wins

n_gpu_layers

Always 999 (all layers on GPU). Single-GPU only — we never split across cards in this tier. The literal -1 works equally well in llama.cpp but 999 is unambiguous and survives clamping in older builds.

split_mode / main_gpu

Always "none" / 0. We never multi-GPU.

cache_type_k / cache_type_v

• Ampere (3090): q8_0 / q4_polar. The q4_polar Polar-quant V kernel exists for sm_86 but the qjl1_256 K kernel does not — fall back to Q8 K.
• Ada / Blackwell / Hopper (4090 / 5090 / H200): qjl1_256 / q4_polar. Both kernels are pre-built and exposed in CAPABILITIES.json.

ctx_checkpoints / ctx_checkpoint_interval

Used by the voice optimistic-rollback path. Mid-prefill snapshots cost ~per-checkpoint = slot_kv_at_checkpoint. Defaults per ctxCheckpointsForTier() in packages/shared/src/local-inference/catalog.ts:

Bundle	ctx_checkpoints	interval
0.8B / 2B	4	4 096
4B / 9B	8	8 192
27B (incl. 256k)	16	8 192

DFlash draft range

Per-card, picked from dflashDraftMin / dflashDraftMax in gpu-profiles.ts:

Card	min	max
3090	4	16
4090	4	24
5090	4	24
H200	8	32

Draft window scales with compute throughput, not memory. Bigger cards can verify a longer drafter run per round without latency hit.

p_min / draft_p_min

0.5 everywhere — drafter token accepted only if p ≥ 0.5. This is a conservative default for voice latency. Higher values mean fewer accepted drafts; lower values raise rollback waste.

Known limits

• 3090 has no FP8 — 27B quality drops slightly without FP8 attention; we keep Q8K KV for safety. Don't promise FP8 on sm_86.
• 5090 sm_120 kernel coverage — early Blackwell llama.cpp builds may not ship qjl1_256 for sm_120. The runtime probes CAPABILITIES.json; missing → fall back to q8_0/q4_0 and surface a structured warning rather than silently. Don't fix in the autotune; fix in the kernel build.
• flash-attn-3 — Hopper only (sm_90). 4090 / 5090 use flash-attn-2.
• 24 GiB cards at 27B + ≥64k ctx — fits only with QJL+Polar AND single slot AND --mlock. Beyond 64k, opt-in kvSpillToCpu=true.
• H200 256k @ 6 parallel — radix cache helps when sessions share a long system prefix; otherwise fresh conversations should be scheduled conservatively to avoid KV pressure.

Override mechanism

The autotune helper merges in this order (later wins):

1. gpu-profiles.ts static profile defaults
2. packages/inference/configs/gpu/<id>.json (this directory)
3. Bundle-specific override block (bundle_recommendations.<bundle>)
4. Per-call overrides arg to selectGpuConfig() (used by the CLI)
5. Env vars: ELIZA_LOCAL_* (see dflash-server.ts for the full list, e.g. ELIZA_LOCAL_UBATCH_SIZE, ELIZA_LOCAL_N_PARALLEL).

When selectGpuConfig() gets a GPU it doesn't recognize, it falls back on a VRAM bucket:

VRAM (GiB)	Bucket	Falls back to
< 12	tiny	Returns null — use catalog defaults
12 – 18	small	RTX 3090 profile, parallel halved
18 – 28	mid	RTX 3090
28 – 40	mid-plus	RTX 5090 (capped)
40 – 80	large	RTX 5090
≥ 80	huge	H200

Bucket fallback is "best effort" — if the user has an unsupported card, log the fallback choice loudly so they know they're not on a tuned profile.