On Wed, Sep 5, 2018 at 4:25 PM Ján Tomko <jto...@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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