AMD MI50 GPU: 150W power limit is the sweet spot for speed vs heat
Someone tested different on an AMD Instinct MI50 GPU (16GB memory) while running the Qwen3.5-9B model (Q4_K_M quantized, about 5.4GB, 32K context) locally using llama.cpp and ROCm 7.2.4. Starting from a default 100W power cap (an energy-saving setup), raising the limit to 150W gave a 19% speedup in text generation with only a small increase in heat.
Pushing further to the card's full 250W limit added only about 12% more speed on top of that, while drawing much more power. So 150W turned out to be the best balance of speed versus heat and power draw.
The tests ran on an HP Z440 with Fedora 44, using a custom cooling setup where an RP2040-Zero board (a small board) automatically adjusts fan speed based on live GPU readings. Each power setting was tested three times with the same prompt at a room of 24°C.
Key points
- Raising the power limit from 100W to 150W gave a 19% speedup in text generation
- Going further to 250W (the card's max) only added about 12% more speed, with much higher power draw
- 150W was the best balance between speed and heat/power efficiency
- Built a custom cooling setup where an RP2040-Zero board auto-adjusts fan speed based on GPU
- Ran the Qwen3.5-9B model locally using llama.cpp and ROCm 7.2.4