Re: [PATCH 2/4] Expand the steal time msr to also contain the consignedtime.

[Michael Wolf]

On 02/06/2013 03:14 PM, Rik van Riel wrote:
> On 02/05/2013 04:49 PM, Michael Wolf wrote:
> > Expand the steal time msr to also contain the consigned time.
> >
> > Signed-off-by: Michael Wolf <mjw@xxxxxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/include/asm/paravirt.h       |    4 ++--
> >   arch/x86/include/asm/paravirt_types.h |    2 +-
> >   arch/x86/kernel/kvm.c                 |    7 ++-----
> >   kernel/sched/core.c                   |   10 +++++++++-
> >   kernel/sched/cputime.c                |    2 +-
> >   5 files changed, 15 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/paravirt.h 
> > b/arch/x86/include/asm/paravirt.h
> > index 5edd174..9b753ea 100644
> > --- a/arch/x86/include/asm/paravirt.h
> > +++ b/arch/x86/include/asm/paravirt.h
> > @@ -196,9 +196,9 @@ struct static_key;
> >   extern struct static_key paravirt_steal_enabled;
> >   extern struct static_key paravirt_steal_rq_enabled;
> >
> > -static inline u64 paravirt_steal_clock(int cpu)
> > +static inline void paravirt_steal_clock(int cpu, u64 *steal)
> >   {
> > -    return PVOP_CALL1(u64, pv_time_ops.steal_clock, cpu);
> > +    PVOP_VCALL2(pv_time_ops.steal_clock, cpu, steal);
> >   }
>
> This may be a stupid question, but what happens if a KVM
> guest with this change, runs on a kernel that still has
> the old steal time interface?
>
> What happens if the host has the new steal time interface,
> but the guest uses the old interface?
>
> Will both cases continue to work as expected with your
> patch series?
>
> If so, could you document (in the source code) why things
> continue to work?
I will test the scenarios you suggest and will report back the results.

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