Re: [Xen-users] Xen dom0 vCPUs pinning for PV/HVM domUs

[John Naggets <hostingnuggets@xxxxxxxxx>]

Thank you Dario for your insight. Indeed I now find the
dom0_vcpus_ping really confusing. In the wiki documentation it says:

"Another interesting approach is pinning Dom0 vCPUs to physical CPUs,
this can be done by adding dom0_vcpus_pin to the Xen command line.
Then once Dom0 has booted you can see to which CPUs the vCPUs have
been pinned and exclude other domains from running on those CPUs."

Source: https://wiki.xenproject.org/wiki/Tuning_Xen_for_Performance#Dom0_vCPUs

I think then this documentation should be adapted to reflect the
reality and not inducing people into confusion.

On Wed, Feb 14, 2018 at 3:01 PM, Dario Faggioli <dfaggioli@xxxxxxxx> wrote:
> On Tue, 2018-02-13 at 15:55 +0100, John Naggets wrote:
>> Thanks Hans for your interesting comments.
>>
>> I forgot to mention that I also have added in my /etc/rc.local the
>> following to be on the safe side:
>>
>> /usr/sbin/xl sched-credit -d 0 -w 512
>>
>> So if I understand here correctly this is a fine config for mixed HVM
>> and PV domUs ensuring enough resources to the dom0?
>>
> Pinning of vCPUs, either of dom0 or domUs, is completely orthogonal to
> what kind of guest is used (for domUs, of course).
>
> Whether pinning or not is helpful, is highly dependent on the actual
> workload, but in general, using dom_vcpus_pin is discouraged (I find
> the parameter itself awkward and confusing).
>
> In fact, in case what you want is to reserve some vCPUs to dom0 and
> dom0 only, using dom0_vcpus_pin _DOES_NOT_ do that.
>
> Regards,
> Dario
> --
> <<This happens because I choose it to happen!>> (Raistlin Majere)
> -----------------------------------------------------------------
> Dario Faggioli, Ph.D, http://about.me/dario.faggioli
> Software Engineer @ SUSE https://www.suse.com/

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