RE: [RFC PATCH v9 4/7] perf stat: Plugin retire_lat value from sampled data to evsel

[Wang, Weilin]

> -----Original Message-----
> From: Namhyung Kim <namhyung@xxxxxxxxxx>
> Sent: Friday, May 24, 2024 4:17 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 v9 4/7] perf stat: Plugin retire_lat value from sampled
> data to evsel
> 
> On Tue, May 21, 2024 at 10:40 AM <weilin.wang@xxxxxxxxx> wrote:
> >
> > From: Weilin Wang <weilin.wang@xxxxxxxxx>
> >
> > In current :R parsing implementation, the parser would recognize events
> with
> > retire_latency modifier and insert them into the evlist like a normal event.
> > Ideally, we need to avoid counting these events.
> >
> > In this commit, at the time when a retire_latency evsel is read, set the retire
> > latency value processed from the sampled data to count value. This sampled
> > retire latency value will be used for metric calculation and final event count
> > print out.
> 
> I'm confused.  Do you mean you don't count the event with 'R' modifier
> (w/ perf stat) and just print the (average) retire latency (from perf record)?

In metric formulas, event without 'R' modifier is included as a normal event already. 
So we don't need to count the event that with 'R' modifier. They only need to be 
sampled. 

> 
> >
> > Signed-off-by: Weilin Wang <weilin.wang@xxxxxxxxx>
> > ---
> >  tools/perf/arch/x86/util/evlist.c |  6 +++++
> >  tools/perf/util/evsel.c           | 44 +++++++++++++++++++++++++++++++
> >  tools/perf/util/evsel.h           |  5 ++++
> >  3 files changed, 55 insertions(+)
> >
> > diff --git a/tools/perf/arch/x86/util/evlist.c
> b/tools/perf/arch/x86/util/evlist.c
> > index b1ce0c52d88d..cebdd483149e 100644
> > --- a/tools/perf/arch/x86/util/evlist.c
> > +++ b/tools/perf/arch/x86/util/evlist.c
> > @@ -89,6 +89,12 @@ int arch_evlist__cmp(const struct evsel *lhs, const
> struct evsel *rhs)
> >                         return 1;
> >         }
> >
> > +       /* Retire latency event should not be group leader*/
> 
> Hmm.. why?
Because we don't want to count them. Make them the group leader would not work. 

> 
> > +       if (lhs->retire_lat && !rhs->retire_lat)
> > +               return 1;
> > +       if (!lhs->retire_lat && rhs->retire_lat)
> > +               return -1;
> > +
> >         /* Default ordering by insertion index. */
> >         return lhs->core.idx - rhs->core.idx;
> >  }
> > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> > index a0a8aee7d6b9..4d700338fc99 100644
> > --- a/tools/perf/util/evsel.c
> > +++ b/tools/perf/util/evsel.c
> > @@ -58,6 +58,7 @@
> >  #include <internal/xyarray.h>
> >  #include <internal/lib.h>
> >  #include <internal/threadmap.h>
> > +#include "util/intel-tpebs.h"
> >
> >  #include <linux/ctype.h>
> >
> > @@ -1523,6 +1524,40 @@ static int evsel__read_one(struct evsel *evsel,
> int cpu_map_idx, int thread)
> >         return perf_evsel__read(&evsel->core, cpu_map_idx, thread, count);
> >  }
> >
> > +static int evsel__set_retire_lat(struct evsel *evsel, int cpu_map_idx, int
> thread)
> > +{
> > +       struct perf_counts_values *count;
> > +       struct tpebs_retire_lat *t;
> > +       bool found = false;
> > +       __u64 val;
> > +
> > +       count = perf_counts(evsel->counts, cpu_map_idx, thread);
> > +
> > +       list_for_each_entry(t, &tpebs_results, nd) {
> > +               if (!strcmp(t->tpebs_name, evsel->name)) {
> > +                       found = true;
> > +                       break;
> > +               }
> > +       }
> > +
> > +       if (!found)
> > +               return -1;
> > +
> > +       /*
> > +        * Only set retire_latency value to the first CPU and thread.
> > +        */
> > +       if (cpu_map_idx == 0 && thread == 0)
> > +               val = t->val;
> > +       else
> > +               val = 0;
> > +
> > +       count->val = val;
> > +       /* Set ena and run to non-zero */
> > +       count->ena = count->run = 1;
> > +       count->lost = 0;
> 
> So here it seems you discard the actual count of the events
> and replace it with the retire latency.  That means you don't
> need to open the event in perf stat, and probably just have a
> placeholder, right?
> 
> Btw, I think it's better to move this logic to intel-tpebs.c file and
> rename to tpebs_set_retire_lat().

Ian wants this to be here and also suggested me to rename this function to 
evsel__read_retire_lat(). I'm ok with either way.  

Thanks,
Weilin

> 
> 
> > +       return 0;
> > +}
> > +
> >  static void evsel__set_count(struct evsel *counter, int cpu_map_idx, int
> thread,
> >                              u64 val, u64 ena, u64 run, u64 lost)
> >  {
> > @@ -1530,6 +1565,12 @@ static void evsel__set_count(struct evsel
> *counter, int cpu_map_idx, int thread,
> >
> >         count = perf_counts(counter->counts, cpu_map_idx, thread);
> >
> > +       if (counter->retire_lat) {
> 
> if (evsel__is_retire_lat(counter)) ?
> 
> 
> > +               evsel__set_retire_lat(counter, cpu_map_idx, thread);
> > +               perf_counts__set_loaded(counter->counts, cpu_map_idx, thread,
> true);
> > +               return;
> > +       }
> > +
> >         count->val    = val;
> >         count->ena    = ena;
> >         count->run    = run;
> > @@ -1778,6 +1819,9 @@ int evsel__read_counter(struct evsel *evsel, int
> cpu_map_idx, int thread)
> >         if (evsel__is_tool(evsel))
> >                 return evsel__read_tool(evsel, cpu_map_idx, thread);
> >
> > +       if (evsel__is_retire_lat(evsel))
> > +               return evsel__set_retire_lat(evsel, cpu_map_idx, thread);
> > +
> 
> I'm not sure if it works well with group event.  Probably that's
> why you wanted to prevent group leaders.  But I guess you
> can just check this after the PERF_FORMAT_GROUP, no?
> 
> Thanks,
> Namhyung
> 
> 
> >         if (evsel->core.attr.read_format & PERF_FORMAT_GROUP)
> >                 return evsel__read_group(evsel, cpu_map_idx, thread);
> >
> > diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
> > index bd8e84954e34..aaf572317e92 100644
> > --- a/tools/perf/util/evsel.h
> > +++ b/tools/perf/util/evsel.h
> > @@ -303,6 +303,11 @@ static inline bool evsel__is_tool(const struct evsel
> *evsel)
> >         return evsel->tool_event != PERF_TOOL_NONE;
> >  }
> >
> > +static inline bool evsel__is_retire_lat(const struct evsel *evsel)
> > +{
> > +       return evsel->retire_lat;
> > +}
> > +
> >  const char *evsel__group_name(struct evsel *evsel);
> >  int evsel__group_desc(struct evsel *evsel, char *buf, size_t size);
> >
> > --
> > 2.43.0
> >