Re: [PATCH v4 04/10] perf stat-shadow: Read tool events directly

[Namhyung Kim <namhyung@kernel.org>]

On Mon, Nov 17, 2025 at 08:36:34PM -0800, Ian Rogers wrote:
> On Mon, Nov 17, 2025 at 6:30 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > On Thu, Nov 13, 2025 at 10:05:10AM -0800, Ian Rogers wrote:
> > > When reading time values for metrics don't use the globals updated in
> > > builtin-stat, just read the events as regular events. The only
> > > exception is for time events where nanoseconds need converting to
> > > seconds as metrics assume time metrics are in seconds.
> > >
> > > Signed-off-by: Ian Rogers <irogers@google.com>
> > > ---
[SNIP]
> > > -                     case TOOL_PMU__EVENT_SYSTEM_TIME:
> > > -                             stats = &ru_stats.ru_stime_usec_stat;
> > > -                             scale = 1e-6;
> > > -                             break;
> >
> > I think this was broken as it seems to be converted to nsec in the
> > update_rusage_stats().
> 
> The global utime/stime is in usecs as in the name. In the tool_pmu it
> is converted to nanoseconds, for consistency with duration_time. In
> the new code the counters are all in nanoseconds and so the same
> scaling factor can be applied.

What do you mean by global utime/stime?

> 
> > > -                     case TOOL_PMU__EVENT_NONE:
> > > -                             pr_err("Invalid tool event 'none'");
> > > -                             abort();
> > > -                     case TOOL_PMU__EVENT_MAX:
> > > -                             pr_err("Invalid tool event 'max'");
> > > -                             abort();
> > > -                     case TOOL_PMU__EVENT_HAS_PMEM:
> > > -                     case TOOL_PMU__EVENT_NUM_CORES:
> > > -                     case TOOL_PMU__EVENT_NUM_CPUS:
> > > -                     case TOOL_PMU__EVENT_NUM_CPUS_ONLINE:
> > > -                     case TOOL_PMU__EVENT_NUM_DIES:
> > > -                     case TOOL_PMU__EVENT_NUM_PACKAGES:
> > > -                     case TOOL_PMU__EVENT_SLOTS:
> > > -                     case TOOL_PMU__EVENT_SMT_ON:
> > > -                     case TOOL_PMU__EVENT_SYSTEM_TSC_FREQ:
> > > -                     case TOOL_PMU__EVENT_CORE_WIDE:
> > > -                     case TOOL_PMU__EVENT_TARGET_CPU:
> > > -                     default:
> > > -                             pr_err("Unexpected tool event '%s'", evsel__name(metric_events[i]));
> > > -                             abort();
> > >                       }
> > > -                     val = avg_stats(stats) * scale;
> > > -                     source_count = 1;
> > > -             } else {
> > > -                     struct perf_stat_evsel *ps = metric_events[i]->stats;
> > > -                     struct perf_stat_aggr *aggr;
> > > -
> > > +             }
> > > +             /* Time events are always on CPU0, the first aggregation index. */
> > > +             aggr = &ps->aggr[is_tool_time ? tool_aggr_idx : aggr_idx];
> > > +             if (!aggr || !metric_events[i]->supported) {
> > >                       /*
> > > -                      * If there are multiple uncore PMUs and we're not
> > > -                      * reading the leader's stats, determine the stats for
> > > -                      * the appropriate uncore PMU.
> > > +                      * Not supported events will have a count of 0, which
> > > +                      * can be confusing in a metric. Explicitly set the
> > > +                      * value to NAN. Not counted events (enable time of 0)
> > > +                      * are read as 0.
> > >                        */
> > > -                     if (evsel && evsel->metric_leader &&
> > > -                         evsel->pmu != evsel->metric_leader->pmu &&
> > > -                         mexp->metric_events[i]->pmu == evsel->metric_leader->pmu) {
> > > -                             struct evsel *pos;
> > > -
> > > -                             evlist__for_each_entry(evsel->evlist, pos) {
> > > -                                     if (pos->pmu != evsel->pmu)
> > > -                                             continue;
> > > -                                     if (pos->metric_leader != mexp->metric_events[i])
> > > -                                             continue;
> > > -                                     ps = pos->stats;
> > > -                                     source_count = 1;
> > > -                                     break;
> > > -                             }
> > > -                     }
> > > -                     aggr = &ps->aggr[aggr_idx];
> > > -                     if (!aggr)
> > > -                             break;
> > > -
> > > -                     if (!metric_events[i]->supported) {
> > > -                             /*
> > > -                              * Not supported events will have a count of 0,
> > > -                              * which can be confusing in a
> > > -                              * metric. Explicitly set the value to NAN. Not
> > > -                              * counted events (enable time of 0) are read as
> > > -                              * 0.
> > > -                              */
> > > -                             val = NAN;
> > > -                             source_count = 0;
> > > -                     } else {
> > > -                             val = aggr->counts.val;
> > > -                             if (!source_count)
> > > -                                     source_count = evsel__source_count(metric_events[i]);
> > > -                     }
> > > +                     val = NAN;
> > > +                     source_count = 0;
> > > +             } else {
> > > +                     val = aggr->counts.val;
> > > +                     if (is_tool_time)
> > > +                             val *= 1e-9; /* Convert time event nanoseconds to seconds. */
> >
> > And this code treats all time events are in nsec now.
> 
> That's correct: user_time, system_time and duration_time are all
> counters that give a count in nanoseconds. However, in the metrics, I
> guess as the counts are doubles, the time has always been in whole
> seconds.

Yep, I think it's ok.

Thanks,
Namhyung