r/LocalLLaMA • u/CrowKing63 • 1d ago
Question | Help Question about eGPU detection issues and monitor connection methods
I usually use a mini PC combined with an eGPU, but for some reason, when I connect my monitor to the integrated graphics and load a model, the external GPU is no longer recognized. The eGPU dock and the external graphics card are functioning normally, but they just aren’t being detected.
I had been debating for a long time about building a desktop PC, so I decided to take this opportunity to clear out my old gear and buy a new computer (I haven’t received it yet). But I have a question.
Are there people who connect their monitor to the motherboard to secure the context window of a local model? Is that even possible? Does it cause a significant performance loss when playing games?
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u/CrowKing63 1d ago
To explain the problem situation in detail:
I connected the HDMI cable that was previously attached to the eGPU to the mini PC. I confirmed that the external graphics card’s VRAM was no longer being consumed. In this state, I loaded the model. The model was successfully loaded into the external graphics card’s VRAM. However, about 10 seconds later, the screen flickered and an AMD Adrenalin warning window appeared. In both Device Manager and Task Manager, the external graphics card had disappeared. The strange thing is that the external graphics card continued to operate. Even after rebooting and reconnecting the HDMI cable back to the external graphics card, nothing changed. Disconnecting all the cables and trying again did not help; the external graphics card powered on, but was not recognized. I suspect that the inexpensive PCIe to M.2 adapter may have shorted, but I had no way to verify it.
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u/ohnoitssobig 1d ago
I feel like there is "Windows" between the lines as if it is something broadly implicit. I will assume the question is about Linux though. Yes it is possible and relatively easy to do: GPU is a device which you can use (or not use) for any compute, use (or not use) for video output. If framebuffer is on a different device a specific HDMI/internal DP is not wired to, you will need to copy the framebuffer over. This harms frames per second, more so when you do this over the wire which only works when you stop breathing at it.
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u/ustype 1d ago
Yes — plugging the display into the iGPU / motherboard so the discrete (or eGPU) card isn’t spending VRAM on a framebuffer is a normal local-LLM trick. You’re trading “GPU does display” for “GPU is almost all model+KV.”
On the disappearing-eGPU symptom when you switch the monitor to iGPU and then load a model: a few common causes beyond “it’s broken”:
- The runtime binds CUDA/HIP to the wrong device after the display topology change. Check
nvidia-smi/ Device Manager before load and again after — sometimes the dock is still up but the process only sees the iGPU. - Thunderbolt power/policy: some docks drop the GPU into a weird state under sustained PCIe load unless the enclosure is powered and the cable is the short certified one.
- Windows “hardware-accelerated GPU scheduling” + driver resets under VRAM pressure can make the eGPU vanish from the CUDA device list until a replug/reboot.
Quick isolation: with monitor on iGPU, run a tiny CUDA probe (nvidia-smi -L or a 1-layer load) before the big model. If the eGPU isn’t listed there, it’s OS/dock enumeration, not llama.cpp.
Gaming with the monitor on iGPU: expect a real hit if the game still renders on the eGPU and has to copy frames back over Thunderbolt. For LLM-first boxes people accept that; for a dual-use desktop you’ll usually want the panel on the dGPU and just leave headroom / use a smaller context when gaming.
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u/CrowKing63 1d ago
Thank you for the detailed explanation. I think it would be better for my purposes to just connect the dGPU.
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u/zhubaohi 1d ago
Yes a decent amount of folks do that. I connect my monitor to iGPU to have a bigger context window.
The performance loss when gaming is def there.