Gan, Jimmy
3994e29cb0
Full documentation of optimizing two LLMs on a single M5 Max GPU: - KV cache quantization (Q4_0) - Flash attention and batch tuning - Router mode with --models-max 1 - Per-model thread optimization via INI presets - Before/after benchmarks (12→48 t/s on 27B, 23→132 t/s on 35B)
llama.cpp Router Mode on Apple Silicon
Single GPU, two models, zero contention — from 12 t/s to 132 t/s
A practical guide to running multiple LLMs on one Apple Silicon Mac using llama-server router mode, achieving full GPU bandwidth for each model with automatic LRU eviction.
The Problem
Running two llama-server processes on the same GPU causes severe bandwidth contention:
Two separate servers (before):
35B MoE: 23 t/s ← -75% from potential
27B dense: 16 t/s ← -63% from potential
Both models stay permanently loaded, permanently competing for GPU memory bandwidth.
The Solution
A single llama-server with --models-max 1 evicts the idle model from GPU memory, giving full bandwidth to whichever model is active:
Router mode (after):
35B MoE: 132 t/s ← 5.7x faster
27B dense: 48 t/s ← 3.0x faster
Quick Start
# 1. Create model symlinks
mkdir -p ~/.hermes/models-router
ln -sf /path/to/model1.gguf ~/.hermes/models-router/
ln -sf /path/to/model2.gguf ~/.hermes/models-router/
# 2. Create per-model INI preset
cat > ~/.hermes/llama-models.ini << 'EOF'
[*]
flash-attn = on
cache-type-k = q4_0
cache-type-v = q4_0
batch-size = 512
ubatch-size = 128
spec-type = draft-mtp
spec-draft-n-max = 3
[model.Model1]
threads = 14
[model.Model2]
threads = 10
EOF
# 3. Launch router
llama-server \
--models-dir ~/.hermes/models-router \
--models-max 1 \
--models-preset ~/.hermes/llama-models.ini \
--host 0.0.0.0 --port 8085 \
-ngl 99 -c 131072 --mlock \
--metrics
Speed Results (M5 Max 40-core, 128GB)
| Model | Two Servers | Router Mode | Gain |
|---|---|---|---|
| Qwen3.6-35B-A3B-Q8_0 (MoE) | 23 t/s | 132 t/s | 5.7x |
| Qwen3.6-27B-Q8_0 (dense) | 16 t/s | 48 t/s | 3.0x |
Trade-off: ~3-4s model load time when switching models.
Hardware
- Chip: Apple M5 Max (40 GPU cores, 614 GB/s bandwidth)
- RAM: 128 GB Unified Memory
- Software: llama.cpp b9910+, launchd, Hermes Agent
Contents
docs/— Full optimization journey with benchmarks at each stepconfigs/— Launchd plist, INI preset, utility scriptsbenchmarks/— Before/after speed comparison data
License
MIT — use it, share it, productize it.