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Re: [libvirt] [PATCH v2 0/4] Add cpu hotplug support to libvirt.

On Wed, Sep 05, 2012 at 05:19:22PM +0800, Tang Chen wrote:
> Hi Viktor,
> On 09/05/2012 04:54 PM, Viktor Mihajlovski wrote:
> >I posted a comment some time ago about that. If you do not mount the
> >cpuset controller, i.e for RHEL 6 you delete the cpuset line from
> >/etc/cgconfig, the CPU affinity isn't controlled by cgroups any more but
> >uses the old mechanism, which works as expected: take a host CPU offline
> >and it will be removed from the process CPU mask and will show up again
> >after onlining the host CPU.
> >The only issue I currently see is that the display of virsh vcpuinfo and
> >vcpupin is somewhat strange. Using taskset will however show the the
> >correct affinity.
> >
> >I suggest that you try out that approach.
> I saw your comment before. You are quite right.  :)
> But the situation here is there are some other features in libvirt
> using cpuset. For example, emulator-pin feature. If we remove cpuset in
> the system, other features could be unusable.

The emulator pinning code should be made to use sched_setaffinity()
when the cpuset controller is not available, just as we do for the
vCPU pinning.

> And more, I found different cgroups are widely used in libvirt now.
> I don't think removing cgroups from system is a good enough idea, though
> it can be a work around.
> What do you think? :)

Either the kernel fixes the broken cpuset behaviour, or we have to
recommend that people don't use it.

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