[libvirt-users] Domain vCPU threads affinity

[Nikos Anastopoulos]

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).

Thanks,
Nikos

[Ján Tomko]

Post by Nikos Anastopoulos
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

[Nikos Anastopoulos]

Post by Nikos Anastopoulos

Post by Nikos Anastopoulos
Hello,
According to the docs, vcpupin will use either cgroups or

sched_setaffinity

Post by Nikos Anastopoulos
to pin vcpu threads to cpus. How is this decision made?
I observe differences even on different hosts featuring the same version

of

Post by Nikos Anastopoulos
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