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Akusari

Member

Registered: 2019-02-26

Posts: 31

Qemu version 10.2 and high iowaits

Hello,

I would like to ask if anyone is observing high iowait values since qemu version 10.2 comparted to previous version 10.1.x ?
I noticed much higher values at all my VM's (Linux, Windows, FreeBSD) even in idle mode.
I'm using the latest Arch LTS-Kernel.

Regards
Akusari

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Akusari

Member

Registered: 2019-02-26

Posts: 31

Re: Qemu version 10.2 and high iowaits

I found the issue. I'm using libvirt for my VM's. Qemu version 10.2.x seems to have a problem with iothreads!

If a VM libvirt configuration contains like this:

...
  <iothreads>2</iothreads>
  <cputune>
    <vcpupin vcpu='0' cpuset='10'/>
    <vcpupin vcpu='1' cpuset='11'/>
    <vcpupin vcpu='2' cpuset='26'/>
    <vcpupin vcpu='3' cpuset='27'/>
    <emulatorpin cpuset='4'/>
    <iothreadpin iothread='1' cpuset='2'/>
    <iothreadpin iothread='2' cpuset='4'/>
    <emulatorsched scheduler='batch'/>
    <iothreadsched iothreads='1' scheduler='fifo' priority='1'/>
    <iothreadsched iothreads='2' scheduler='fifo' priority='1'/>
  </cputune>
...

IO waits up to 9 will be shown on my system.
If i remove all related iothread stuff everything is smoothly again.

Previous QEMU version 10.1.x doesn't show any kind of such problems.
I guess it's a upstream bug.

Or it could be a problem between libvirt version 12.0 and Qemu 10.2, but libvirt version 12.0 runs fine with Qemu version 10.1.x without iowait problems.

Regards
Akusari

Last edited by Akusari (2026-01-25 23:43:54)

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black listed users: seth WorMzy
Please stay away from this thread - Thanks.