Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics

[Liang, Kan]

On 5/28/2019 9:48 AM, Peter Zijlstra wrote:
> On Tue, May 21, 2019 at 02:40:50PM -0700, kan.liang@xxxxxxxxxxxxxxx wrote:
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index b980b9e95d2a..0d7081434d1d 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -133,6 +133,11 @@ struct hw_perf_event {
> >   
> >   			struct hw_perf_event_extra extra_reg;
> >   			struct hw_perf_event_extra branch_reg;
> > +
> > +			u64		saved_metric;
> > +			u64		saved_slots;
> > +			u64		last_slots;
> > +			u64		last_metric;
>
> This is really sad, and I'm thinking much of that really isn't needed
> anyway, due to how you're not using some of the other fields.

If we don't cache the value, we have to update all metrics events when 
reading any metrics event. I think that could bring high overhead.

Thanks,
Kan
> >   		};
> >   		struct { /* software */
> >   			struct hrtimer	hrtimer;
> > --
> > 2.14.5