[libvirt-users] Domain vCPU threads affinity

[Nikos Anastopoulos]

On Wed, Sep 5, 2018 at 4:25 PM Ján Tomko <jtomko at redhat.com> wrote:

> On Wed, Sep 05, 2018 at 03:48:45PM +0300, Nikos Anastopoulos wrote:
> >Hello,
> >
> >According to the docs, vcpupin will use either cgroups or
> sched_setaffinity
> >to pin vcpu threads to cpus. How is this decision made?
> >I observe differences even on different hosts featuring the same version
> of
> >libvirtd (1.3.1): on one host vcpupin affects cpuset.cpus (cgroup), and on
> >the other it affects vcpu threads affinity (observed through taskset).
>
> It affects both affinity and cpuset.cpus.
>
> Are there any differences in the host environment, or the domain XML?
>
> Also note that libvirt 1.3.1 is 2.5 years old now.
>
> Jano
>

Hi Jano,

The domain XMLs are the same.

"host1" is an Ubuntu 16.04.4 LTS with a 4.4.0-130-generic kernel. In this
host vcpupin affects cpuset.cpus.
As an observation, note that any change in cpuset.cpus gets reflected in
task affinity, as well. This is a general behavior, not because of Libvirt
and the way that vcpupin works. The opposite is not true, i.e. changing cpu
affinity via sched_setaffinity will leave cpuset.cpus intact -- and will
fail if you try to specify a cpu not belonging to cpuset.cpus.

"host2" is also an Ubuntu 16.04.4 LTS with 4.4.0-87-generic. In that host
vcpupin affects only task affinities.

Nikos
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