Multi-GPU PCIe Switch Setup Shows Almost No Performance Loss
Old_Grapefruit8774 · reddit · 2026-07-11
The author tested a direct-connect setup for 6 MI50 GPUs on an X99-E-WS motherboard, alongside a hybrid setup using a PEX8749 PCIe switch (4 cards routed through the switch chip, 2 directly connected).
Test Configuration
- Asus X99-E-WS, flashed with a custom BIOS supporting multi-GPU
- Xeon E5-2680 v4
- 128GB DDR4
- Goal: Provide around 1TB VRAM for multi-machine/multi-GPU local AI inference
Results
After multiple runs using llama bench:
- The tg metric typically improved by 0.8%–2.8% under the switch setup
- The pp metric saw less than a 1% loss
- Overall differences across multiple test combinations were minimal, with some scenarios breaking even
Conclusion: On this older platform, hanging部分 GPUs under the PEX8749 switch didn't cause a performance disaster and even yielded slight gains in tg.
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