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References: <20161104094322.GA16930@amt.cnet> <20161104152522.GC5388@potion>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <1c69a083-eef0-8fa0-0e74-5a4e25a066a0@redhat.com>
Date: Fri, 4 Nov 2016 16:33:33 +0100
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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: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>
Cc: kvm@vger.kernel.org, qemu-devel <qemu-devel@nongnu.org>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Juan Quintela <quintela@redhat.com>, Eduardo Habkost <ehabkost@redhat.com>, Roman Kagan <rkagan@virtuozzo.com>



On 04/11/2016 16:25, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote:
>> > =20
>> > +        if (s->advance_clock && s->clock + s->advance_clock > s->cl=
ock) {
>> > +            s->clock +=3D s->advance_clock;
>> > +            s->advance_clock =3D 0;
>> > +        }
> Can't the advance_clock added to the migrated KVMClockState instead of
> passing it as another parameter?
>=20
> (It is sad that we can't just query KVMClockState in kvmclock_pre_save
>  because of the Linux bug.)

What Linux bug?  The one that makes us use kvmclock_current_nsec?

It should work with 4.9-rc (well, once Linus applies my pull request).
4.9-rc will not return ktime_get_ns for KVM_GET_CLOCK; it will return
the raw value from the kernel timekeeper.

I'm thinking that we should add a KVM capability for this, and skip
kvmclock_current_nsec if the capability is present.  The first part is
trivial, so we can do it even during Linux rc period.

Paolo