This may not strictly be VFIO-related but it is latency-related. Feel free to suggest another place to post.

I have a VM which has 4 of the host's 8 cores, and has multiple PCI devices passed through - GPU, audio, USB and SATA.

If I give the vCPU threads RT priority (via libvirt XML), and then run `stress -c 4` on the VM, the host would freeze.

If I dedicate the 4 cores to the VM via isolcpus= and CPU pinning, then the host is okay but there are still other issues, e.g. the guest's audio glitches like crazy.

Everything is fine (well mostly fine) if I refrain from setting RT priority on the vCPU threads.

What's happening here? Is this a scheduling bug?

Host and guest are running kernel 5.4.91, and qemu is stable-5.0.


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