Re: [Xen-devel] [PATCH v4 14/17] x86/VPMU: Save VPMU state for PV guests during context switch

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 02/04/2014 06:38 AM, Jan Beulich wrote:
> > > > On 21.01.14 at 20:08, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> > Save VPMU state during context switch for both HVM and PV guests unless we
> > are in PMU privileged mode (i.e. dom0 is doing all profiling) and the
> > switched
> > out domain is not the control domain. The latter condition is needed because
> > me may have just turned the privileged PMU mode on and thus need to save
> > last domain.
> While this is understandable, ...
>
> > --- a/xen/arch/x86/domain.c
> > +++ b/xen/arch/x86/domain.c
> > @@ -1444,17 +1444,16 @@ void context_switch(struct vcpu *prev, struct vcpu 
> > *next)
> >       }
> >   
> >       if (prev != next)
> > -        update_runstate_area(prev);
> > -
> > -    if ( is_hvm_vcpu(prev) )
> >       {
> > -        if (prev != next)
> > +        update_runstate_area(prev);
> > +        if ( !(vpmu_mode & XENPMU_MODE_PRIV) ||
> > +             !is_control_domain(prev->domain) )
> >               vpmu_save(prev);
> ... I'd really like you to investigate ways to achieve the same effect
> without this extra second condition added to the context switch path.
> E.g. by synchronously issuing a save on all affected vCPU-s when
> privileged mode gets turned on.
Yes, I should do something like that.

-boris


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