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linux-next: new scheduler messages span: 0-15 (max cpu_capacity = 589) when starting KVM guests

From Christian Borntraeger <borntraeger@de.ibm.com>
Newsgroups linux.kernel
Subject linux-next: new scheduler messages span: 0-15 (max cpu_capacity = 589) when starting KVM guests
Date 2016-09-19 15:30 +0200
Message-ID <sj6NX-5YW-7@gated-at.bofh.it> (permalink)
Organization linux.* mail to news gateway

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Dietmar, Ingo, Tejun,

since commit cd92bfd3b8cb0ec2ee825e55a3aee704cd55aea9
   sched/core: Store maximum per-CPU capacity in root domain

I get tons of messages from the scheduler like
[..]
span: 0-15 (max cpu_capacity = 589)
span: 0-15 (max cpu_capacity = 589)
span: 0-15 (max cpu_capacity = 589)
span: 0-15 (max cpu_capacity = 589)
[..]

whenever I start kvm guests with libvirt.

The reason seems to be that libvirt via systemd/machined tries to move all
guest vcpus into its cpuset and for whatever reasons, the way it is done
will always call rebuild_sched_domains from the cgroup code.

While the message alone is somewhat of a nuisance, I think rebuilding
the scheduling domains for moving kvm vcpus is really expensive.

Tejun, do you have an idea whats going on here? Is libvirt using
the cgroup interface wrong (e.g. also d a memory migrate or whatever)

Christian

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linux-next: new scheduler messages span: 0-15 (max cpu_capacity =  589) when starting KVM guests Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-19 15:30 +0200
  Re: linux-next: new scheduler messages span: 0-15 (max cpu_capacity  = 589) when starting KVM guests Peter Zijlstra <peterz@infradead.org> - 2016-09-19 15:50 +0200
    Re: linux-next: new scheduler messages span: 0-15 (max cpu_capacity =  589) when starting KVM guests Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-09-19 16:00 +0200
    Re: linux-next: new scheduler messages span: 0-15 (max cpu_capacity =  589) when starting KVM guests Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-19 16:10 +0200
    Re: linux-next: new scheduler messages span: 0-15 (max cpu_capacity =  589) when starting KVM guests Christian Borntraeger <borntraeger@de.ibm.com> - 2016-09-20 09:50 +0200

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