On Tue, May 28, 2019 at 02:24:56PM -0400, Liang, Kan wrote: > > > On 5/28/2019 9:48 AM, Peter Zijlstra wrote: > > On Tue, May 21, 2019 at 02:40:50PM -0700, [email protected] 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.
Since you don't support sampling, or even 'normal' functionality on this FIXED3/SLOTS thing, you'll not use prev_count, sample_period, last_period, period_left, interrupts_seq, interrupts, freq_time_stamp and freq_count_stamp. So why do you then need to grow the data structure with 4 more nonsense fields? Also, I'm not sure what you need those last things for, you reset the value to 0 every time you read them, there is no delta to track.
