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List:       kvm
Subject:    Re: [Qemu-devel] [PATCH 1/3] target-i386: add a subsection of vcpu's TSC rate in vmstate_x86_cpu
From:       "Dr. David Alan Gilbert" <dgilbert () redhat ! com>
Date:       2015-09-30 8:07:08
Message-ID: 20150930080707.GA2627 () work-vm
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* Haozhong Zhang (haozhong.zhang@intel.com) wrote:
> On Tue, Sep 29, 2015 at 08:00:13PM +0100, Dr. David Alan Gilbert wrote:
> > * Haozhong Zhang (haozhong.zhang@intel.com) wrote:
> > > The newly added subsection 'vmstate_tsc_khz' in this patch results in
> > > vcpu's TSC rate being saved on the source machine and loaded on the
> > > target machine during the migration.
> > > 
> > > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> > 
> > Hi,
> >   I'd appreciate it if you could tie this to only do it on newer
> > machine types; that way it won't break back migration.
> >
> 
> Does "back migration" mean migrating from QEMU w/ vmstate_tsc_khz
> subsection to QEMU w/o that subsection?

Yes; like if we migrate from a newer qemu to an older qemu but with
the same machine type.

Dave

> 
> - Haozhong
> 
> > Dave
> > 
> > > ---
> > >  target-i386/machine.c | 20 ++++++++++++++++++++
> > >  1 file changed, 20 insertions(+)
> > > 
> > > diff --git a/target-i386/machine.c b/target-i386/machine.c
> > > index 9fa0563..80108a3 100644
> > > --- a/target-i386/machine.c
> > > +++ b/target-i386/machine.c
> > > @@ -752,6 +752,25 @@ static const VMStateDescription vmstate_xss = {
> > >      }
> > >  };
> > >  
> > > +static bool tsc_khz_needed(void *opaque)
> > > +{
> > > +    X86CPU *cpu = opaque;
> > > +    CPUX86State *env = &cpu->env;
> > > +
> > > +    return env->tsc_khz != 0;
> > > +}
> > > +
> > > +static const VMStateDescription vmstate_tsc_khz = {
> > > +    .name = "cpu/tsc_khz",
> > > +    .version_id = 1,
> > > +    .minimum_version_id = 1,
> > > +    .needed = tsc_khz_needed,
> > > +    .fields = (VMStateField[]) {
> > > +        VMSTATE_INT64(env.tsc_khz, X86CPU),
> > > +        VMSTATE_END_OF_LIST()
> > > +    }
> > > +};
> > > +
> > >  VMStateDescription vmstate_x86_cpu = {
> > >      .name = "cpu",
> > >      .version_id = 12,
> > > @@ -871,6 +890,7 @@ VMStateDescription vmstate_x86_cpu = {
> > >          &vmstate_msr_hyperv_crash,
> > >          &vmstate_avx512,
> > >          &vmstate_xss,
> > > +        &vmstate_tsc_khz,
> > >          NULL
> > >      }
> > >  };
> > > -- 
> > > 2.4.8
> > > 
> > > 
> > --
> > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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