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[Qemu-discuss] KVM+Qemu with PCI passthrough of GPU and USB responsible

From: Christopher Snowhill
Subject: [Qemu-discuss] KVM+Qemu with PCI passthrough of GPU and USB responsible for high CPU usage?
Date: Mon, 18 Dec 2017 17:17:43 -0800

I have two Qemu VMs on my Linux host machine, overutilizing the host CPU, a 
Core i7 3770, and allocated 16GB and 8GB of the total 32GB of RAM using 

Something I notice about these VMs is that one of them, using nothing but 
virtual resources, its main process uses 3-6% of CPU resources when the machine 
is idling. The VM with the GPU and USB passthrough uses 45-67% on its main 
process when idle, and when I'm logged in locally, using the session at an 
attached monitor, it uses 250-350%, which is in contention with the 8 threads I 
gave to that VM.

Is this normal for the amount of IO incurred by passing through a GPU?

As an aside, I also have an issue with the XHCI controller not supporting 
reset, and occasionally, guest reboots of that VM, or stopping and restarting 
the Qemu instance completely, causing the host machine to lock up. Naturally, I 
can't SysRq magic key it even if it is still alive, as I have passed all 
attached USB interfaces to the VM, and it has no PS/2 ports.

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