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Date: Fri, 4 Nov 2016 16:31:41 -0200
From: Marcelo Tosatti <mtosatti@redhat.com>
Message-ID: <20161104183137.GA13662@amt.cnet>
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Subject: Re: [Qemu-devel] [QEMU PATCH] kvmclock: advance clock by time
 window between vm_stop and pre_save
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To: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org, qemu-devel <qemu-devel@nongnu.org>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Juan Quintela <quintela@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>

On Fri, Nov 04, 2016 at 06:39:18PM +0100, Radim Kr=C4=8Dm=C3=A1=C5=99 wro=
te:
> 2016-11-04 15:07-0200, Marcelo Tosatti:
> > On Fri, Nov 04, 2016 at 04:25:23PM +0100, Radim Kr=C4=8Dm=C3=A1=C5=99=
 wrote:
> >> > +        /*
> >> > +         * Transition from VM-running to VM-stopped via migration=
?
> >> > +         * Record when the VM was stopped.
> >> > +         */
> >> > +
> >> > +        if (state =3D=3D RUN_STATE_FINISH_MIGRATE &&
> >> > +            !migration_in_postcopy(migrate_get_current())) {
> >> > +            clock_gettime(CLOCK_MONOTONIC, &s->t_aftervmstop);
> >>=20
> >> How big (more like small) was the clock delta between here and
> >> kvmclock_pre_save with postcopy?
> >>=20
> >> Thanks.
> >=20
> > qemu-system-x86_64: postcopy_ram_supported_by_host: userfaultfd not
> > available: Function not implemented
> >=20
> > But should be about the same as precopy+this patch (guess as i don't=20
> > know the postcopy path).
>=20
> I was wondering about the improvement we could achieve by not excluding
> postcopy from the time fixup.  (i.e. how much time elapses between
> pausing and migrating the vm in postcopy)
>=20
> I would also guess that it is not significant.

Ideally the total should be zero because for certain workloads
any change is problematic...=20