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Re: [PATCH-for-4.17] xen/sched: fix restore_vcpu_affinity() by removing it
- To: Juergen Gross <jgross@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Dario Faggioli <dfaggioli@xxxxxxxx>
- Date: Fri, 21 Oct 2022 09:16:03 +0000
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, "julien@xxxxxxx" <julien@xxxxxxx>, "wl@xxxxxxx" <wl@xxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, "marmarek@xxxxxxxxxxxxxxxxxxxxxx" <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, "george.dunlap@xxxxxxxxxx" <george.dunlap@xxxxxxxxxx>, "andrew.cooper3@xxxxxxxxxx" <andrew.cooper3@xxxxxxxxxx>, "Henry.Wang@xxxxxxx" <Henry.Wang@xxxxxxx>
- Delivery-date: Fri, 21 Oct 2022 09:16:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHY5Rp63crRdqzTYU65u4+DFjIN7K4YbPgAgAAkTQA=
- Thread-topic: [PATCH-for-4.17] xen/sched: fix restore_vcpu_affinity() by removing it
On Fri, 2022-10-21 at 09:06 +0200, Juergen Gross wrote:
> On 21.10.22 08:58, Juergen Gross wrote:
> > When the system is coming up after having been suspended,
> > restore_vcpu_affinity() is called for each domain in order to
> > adjust
> > the vcpu's affinity settings in case a cpu didn't come to live
> > again.
> >
> > The way restore_vcpu_affinity() is doing that is wrong, because the
> > specific scheduler isn't being informed about a possible migration
> > of
> > the vcpu to another cpu. Additionally the migration is often even
> > happening if all cpus are running again, as it is done without
> > check
> > whether it is really needed.
> >
> > As cpupool management is already calling cpu_disable_scheduler()
> > for
> > cpus not having come up again, and cpu_disable_scheduler() is
> > taking
> > care of eventually needed vcpu migration in the proper way, there
> > is
> > simply no need for restore_vcpu_affinity().
> >
> > So just remove restore_vcpu_affinity() completely.
> >
> > Fixes: 8a5d50dd0b04 ("xen: sched: simplify ACPI S3 resume path.")
>
> This Fixes: tag is wrong. It should be:
>
> Fixes: 8a04eaa8ea83 ("xen/sched: move some per-vcpu items to struct
> sched_unit")
>
Acked-by: Dario Faggioli <dfaggioli@xxxxxxxx>
Thanks and Regards
--
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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