trying to understand steal time with cpu pinning

Sean Mooney smooney at
Thu Jul 11 12:03:28 UTC 2019

On Thu, 2019-07-11 at 06:15 +0000, Manuel Sopena Ballesteros wrote:
> Dear Openstack community,
> Please correct me if I am wrong.
> As far as I understand `steal time > 0` means that the hypervisor has replaced a vcpu with a different one on the
> physical cpu.
> Also, cpu pinning allocates a vcpu to a physical cpu permanently.
> I have a vm setup with cpu pinning and numa affinity and realized, that cpu steal time is between 1% and 0%.
> Why is that?
there are 2 ways that this can happen.
1.) you are not setting hw:emulator_thread_policy to move the qemu emulator threads to a different core.
2.) you have host system process or kernel threads that are stealing guest cpu time like vhost threads.

you can prevent 2 using systemd or take teh blunt hammer approch and use the kernel isolcpus parmater
but that generally should only be used for realtime systems.

openstack does not prevent other host process form running on the vcpu_pin_set, that is left to the
operator/installer/os to do.

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