[Qemu-devel] [Bug 1174654] Re: qemu-system-x86_64 takes 100% CPU after host machine resumed from suspend to ram

[Francois Gouget]

This sounds sort of like a problem I have with reverting to live snapshots.
What I found out is that this is related to restoring the clock in the guest. 
You can find out more about it there:
https://bugs.launchpad.net/qemu/+bug/1505041

The takeaway is that a workaround is to set track='guest' on the rtc
timer. For instance:

    <clock offset='localtime'>
      <timer name='rtc' track='guest'/>
    </clock>

If you have track='catchup' QEMU seems to try to send millions of
interrupts so the guest clock will catch up to the current time, which
can take minutes during which the guest is unusable.

It is possible this no longer happens though as I have had this
workaround in place for quite some time but nobody formally said this is
fixed or pointed to a commit fixing this.

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https://bugs.launchpad.net/bugs/1174654

Title:
  qemu-system-x86_64 takes 100% CPU after host machine resumed from
  suspend to ram

Status in QEMU:
  Confirmed
Status in qemu package in Ubuntu:
  Invalid

Bug description:
  I have Windows XP SP3  inside qemu VM. All works fine in 12.10. But
  after upgraiding to 13.04 i have to restart the VM each time i
  resuming my host machine, because qemu process starts to take CPU
  cycles and OS inside VM is very slow and sluggish. However it's still
  controllable and could be shutdown by itself.

  According to the taskmgr any active process takes 99% CPU. It's not
  stuck on some single process.

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