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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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