Re: [PATCH v2] perf stat: Hide invalid uncore event output for aggr mode

[Ian Rogers]

On Wed, Jan 25, 2023 at 11:24 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> The current display code for perf stat iterates given cpus and build the
> aggr map to collect the event data for the aggregation mode.
>
> But uncore events have their own cpu maps and it won't guarantee that
> it'd match to the aggr map.  For example, per-package uncore events
> would generate a single value for each socket.  When user asks per-core
> aggregation mode, the output would contain 0 values for other cores.
>
> Thus it needs to check the uncore PMU's cpumask and if it matches to the
> current aggregation id.
>
> Before:
>   $ sudo ./perf stat -a --per-core -e power/energy-pkg/ sleep 1
>
>    Performance counter stats for 'system wide':
>
>   S0-D0-C0              1               3.73 Joules power/energy-pkg/
>   S0-D0-C1              0      <not counted> Joules power/energy-pkg/
>   S0-D0-C2              0      <not counted> Joules power/energy-pkg/
>   S0-D0-C3              0      <not counted> Joules power/energy-pkg/
>
>          1.001404046 seconds time elapsed
>
>   Some events weren't counted. Try disabling the NMI watchdog:
>         echo 0 > /proc/sys/kernel/nmi_watchdog
>         perf stat ...
>         echo 1 > /proc/sys/kernel/nmi_watchdog
>
> The core 1, 2 and 3 should not be printed because the event is handled
> in a cpu in the core 0 only.  With this change, the output becomes like
> below.
>
> After:
>   $ sudo ./perf stat -a --per-core -e power/energy-pkg/ sleep 1
>
>    Performance counter stats for 'system wide':
>
>   S0-D0-C0              1               2.09 Joules power/energy-pkg/
>
> Fixes: b89761351089 ("perf stat: Update event skip condition for system-wide per-thread mode and merged uncore and hybrid events")
> Cc: Athira Jajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
> Cc: Michael Petlan <mpetlan@xxxxxxxxxx>
> Tested-by: Ian Rogers <irogers@xxxxxxxxxx>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Acked-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> ---
> * rename to 'should_skip_zero_counter'
> * check pmu->cpus instead
> * add kernel-doc style comments
> * add Ian's Tested-by tag
>
>  tools/perf/util/stat-display.c | 51 ++++++++++++++++++++++++++++++----
>  1 file changed, 46 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> index 8bd8b0142630..1b5cb20efd23 100644
> --- a/tools/perf/util/stat-display.c
> +++ b/tools/perf/util/stat-display.c
> @@ -787,6 +787,51 @@ static void uniquify_counter(struct perf_stat_config *config, struct evsel *coun
>                 uniquify_event_name(counter);
>  }
>
> +/**
> + * should_skip_zero_count() - Check if the event should print 0 values.
> + * @config: The perf stat configuration (including aggregation mode).
> + * @counter: The evsel with its associated cpumap.
> + * @id: The aggregation id that is being queried.
> + *
> + * Due to mismatch between the event cpumap or thread-map and the
> + * aggregation mode, sometimes it'd iterate the counter with the map
> + * which does not contain any values.
> + *
> + * For example, uncore events have dedicated CPUs to manage them,
> + * result for other CPUs should be zero and skipped.
> + *
> + * Return: %true if the value should NOT be printed, %false if the value
> + * needs to be printed like "<not counted>" or "<not supported>".
> + */
> +static bool should_skip_zero_counter(struct perf_stat_config *config,
> +                                    struct evsel *counter,
> +                                    const struct aggr_cpu_id *id)
> +{
> +       struct perf_cpu cpu;
> +       int idx;
> +
> +       /*
> +        * Skip value 0 when enabling --per-thread globally,
> +        * otherwise it will have too many 0 output.
> +        */
> +       if (config->aggr_mode == AGGR_THREAD && config->system_wide)
> +               return true;
> +       /*
> +        * Skip value 0 when it's an uncore event and the given aggr id
> +        * does not belong to the PMU cpumask.
> +        */
> +       if (!counter->pmu || !counter->pmu->is_uncore)
> +               return false;
> +
> +       perf_cpu_map__for_each_cpu(cpu, idx, counter->pmu->cpus) {
> +               struct aggr_cpu_id own_id = config->aggr_get_id(config, cpu);
> +
> +               if (aggr_cpu_id__equal(id, &own_id))
> +                       return false;
> +       }
> +       return true;
> +}
> +
>  static void print_counter_aggrdata(struct perf_stat_config *config,
>                                    struct evsel *counter, int s,
>                                    struct outstate *os)
> @@ -814,11 +859,7 @@ static void print_counter_aggrdata(struct perf_stat_config *config,
>         ena = aggr->counts.ena;
>         run = aggr->counts.run;
>
> -       /*
> -        * Skip value 0 when enabling --per-thread globally, otherwise it will
> -        * have too many 0 output.
> -        */
> -       if (val == 0 && config->aggr_mode == AGGR_THREAD && config->system_wide)
> +       if (val == 0 && should_skip_zero_counter(config, counter, &id))
>                 return;
>
>         if (!metric_only) {
> --
> 2.39.1.456.gfc5497dd1b-goog
>