RE: [RFC PATCH v10 0/8] TPEBS counting mode support

[Wang, Weilin]

> -----Original Message-----
> From: Namhyung Kim <namhyung@xxxxxxxxxx>
> Sent: Friday, May 31, 2024 2:30 PM
> To: Wang, Weilin <weilin.wang@xxxxxxxxx>
> Cc: Ian Rogers <irogers@xxxxxxxxxx>; Arnaldo Carvalho de Melo
> <acme@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Ingo Molnar
> <mingo@xxxxxxxxxx>; Alexander Shishkin
> <alexander.shishkin@xxxxxxxxxxxxxxx>; Jiri Olsa <jolsa@xxxxxxxxxx>; Hunter,
> Adrian <adrian.hunter@xxxxxxxxx>; Kan Liang <kan.liang@xxxxxxxxxxxxxxx>;
> linux-perf-users@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Taylor, Perry
> <perry.taylor@xxxxxxxxx>; Alt, Samantha <samantha.alt@xxxxxxxxx>; Biggers,
> Caleb <caleb.biggers@xxxxxxxxx>
> Subject: Re: [RFC PATCH v10 0/8] TPEBS counting mode support
> 
> On Fri, May 31, 2024 at 12:00 AM Wang, Weilin <weilin.wang@xxxxxxxxx>
> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Namhyung Kim <namhyung@xxxxxxxxxx>
> > > Sent: Thursday, May 30, 2024 11:37 PM
> > > To: Wang, Weilin <weilin.wang@xxxxxxxxx>
> > > Cc: Ian Rogers <irogers@xxxxxxxxxx>; Arnaldo Carvalho de Melo
> > > <acme@xxxxxxxxxx>; Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Ingo Molnar
> > > <mingo@xxxxxxxxxx>; Alexander Shishkin
> > > <alexander.shishkin@xxxxxxxxxxxxxxx>; Jiri Olsa <jolsa@xxxxxxxxxx>; Hunter,
> > > Adrian <adrian.hunter@xxxxxxxxx>; Kan Liang <kan.liang@xxxxxxxxxxxxxxx>;
> > > linux-perf-users@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Taylor,
> Perry
> > > <perry.taylor@xxxxxxxxx>; Alt, Samantha <samantha.alt@xxxxxxxxx>;
> Biggers,
> > > Caleb <caleb.biggers@xxxxxxxxx>
> > > Subject: Re: [RFC PATCH v10 0/8] TPEBS counting mode support
> > >
> > > Hello,
> > >
> > > On Tue, May 28, 2024 at 11:43 PM <weilin.wang@xxxxxxxxx> wrote:
> > > >
> > > > From: Weilin Wang <weilin.wang@xxxxxxxxx>
> > > >
> > > > I have tried not to count retire_latency events but did not succeed.
> > > > In particular, I tried the following methods:
> > > >  - Convert retire_latency event to dummy event in event parser.
> > > >  - Early bail out in evsel__open_cpu() and store_evsel_ids().
> > > >
> > > > The first method fails and causes non-retire_latency events with the same
> > > event
> > > > name return 0 count.
> > > >
> > > > The second method fails and causes all the events in the same group
> > > returning
> > > > "<not counted>" results.
> > >
> > > Can you please describe where it fails?  Is it failing on other events
> > > because the tpebs event is a leader of the group?  I think you wanted
> > > to avoid having it in the leader position.  If we can skip any actual
> > > operations (open/close/enable/disable/read) for the tpebs events, then
> > > it could be fine..
> >
> > It does not fail with the code in this patch set. But if I make it return directly
> > from tpebs_start() in evsel__open_cpu(), it will cause segfault. The segfault is
> > caused by store_evsel_id(). I could add another early return from
> store_evsel_id()
> > if the evsel->retire_lat is true.
> 
> Yeah, I think event:R should not go to kernel from perf stat and you need to
> handle that in the tools.
> 
> >
> > After this change, it will eventually run and give me <not counted> results
> > like below:
> >
> >         <not counted> event1
> >         <not counted> event2
> >         xx event1:R
> >
> > In a different case, it may seem to work (xxxxxx stands for some valid value):
> >
> >         xxxxxxx event1
> >         xxxxxxx event2
> >         xxxxxxx event3
> >         xx event1:R
> >
> > In the first case, the event1, event2 and event1:R are scheduled in the same
> > group. On the other hand, in the second case, event1, event2 and event3
> are
> > in one group, while event1:R is in a different group.
> 
> If you don't open event1:R then the kernel only sees event1 and event2.
> 
> >
> > Based on these two different type of results, I believe the failure happens in
> > the group that include a :R event. I've added the change to
> arch_evlist__cmp()
> > so that a :R event would not be a leader of the group.
> >
> > I think I've made evsel__open_cpu() return before it create fd and make
> > store_evsel_id() not to read and store fd. I'm not sure where I'm missing.
> Please
> > let me know if you have any suggestions.
> 
> As I said, please don't open event1:R (for perf stat) and let tpebs_stop() set
> the value using the data from perf record in background.

I think this is exactly what I'm trying to achieve, not open event1:R for perf stat. 
The problem is that I'm not sure how to do it properly in the code. Please give 
me some suggestion here. 

Thanks,
Weilin

> 
> Thanks,
> Namhyung