Re: [RFC PATCH v3 11/18] perf stat: Add function to handle special events in hardware-grouping

[Ian Rogers]

On Tue, Dec 12, 2023 at 3:03 PM <weilin.wang@xxxxxxxxx> wrote:
>
> From: Weilin Wang <weilin.wang@xxxxxxxxx>
>
> There are some special events like topdown events and TSC that are not
> decribed in pmu-event JSON files. Add support to handle this type of

nit: described.

> events. This should be considered as a temporary solution because including
> these events in JSON files would be a better solution.

Agreed on this being temporary. We have a similar hack with
arch_evsel__must_be_in_group, could that be reused here?
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/arch/x86/util/evsel.c?h=perf-tools-next#n41
It doesn't cover TSC but parse-events makes TSC a separate group
during parsing as the PMU (msr) differs from the PMU of the events
(typically cpu). Fixing the metrics and events to be json is very
do-able. I see on Icelake, for example, TOPDOWN.BACKEND_BOUND_SLOTS is
available while frontend isn't.

As an aside, we may want to treat msr as a software pmu:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmu.c?h=perf-tools-next#n1761
which may be a metric regression.

Thanks,
Ian

> Signed-off-by: Weilin Wang <weilin.wang@xxxxxxxxx>
> ---
>  tools/perf/util/metricgroup.c | 25 +++++++++++++++++++++++--
>  tools/perf/util/metricgroup.h | 15 +++++++++++++++
>  2 files changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> index 5d9ed22963be..03383f820e06 100644
> --- a/tools/perf/util/metricgroup.c
> +++ b/tools/perf/util/metricgroup.c
> @@ -2023,6 +2023,15 @@ static int create_grouping(struct list_head *pmu_info_list,
>         return ret;
>  };
>
> +static bool is_special_event(const char *id)
> +{
> +       for (int i = 0; i < SPECIAL_EVENT_MAX; i++) {
> +               if (!strncmp(id, special_event_names[i], strlen(special_event_names[i])))
> +                       return true;
> +       }
> +       return false;
> +}
> +
>  /**
>   * hw_aware_build_grouping - Build event groupings by reading counter
>   * requirement of the events and counter available on the system from
> @@ -2047,7 +2056,17 @@ static int hw_aware_build_grouping(struct expr_parse_ctx *ctx __maybe_unused,
>         hashmap__for_each_entry(ctx->ids, cur, bkt) {
>                 const char *id = cur->pkey;
>
> -               pr_debug("found event %s\n", id);
> +               if (is_special_event(id)) {
> +                       struct metricgroup__event_info *event;
> +
> +                       event = event_info__new(id, "default_core", "0",
> +                                               /*free_counter=*/true);
> +                       if (!event)
> +                               goto err_out;
> +
> +                       list_add(&event->nd, &event_info_list);
> +                       continue;
> +               }
>                 ret = get_metricgroup_events(id, etable, &event_info_list);
>                 if (ret)
>                         goto err_out;
> @@ -2519,8 +2538,10 @@ int metricgroup__parse_groups(struct evlist *perf_evlist,
>                 ret = hw_aware_parse_groups(perf_evlist, pmu, str,
>                             metric_no_threshold, user_requested_cpu_list, system_wide,
>                             /*fake_pmu=*/NULL, metric_events, table);
> -               if (!ret)
> +               if (!ret) {
> +                       pr_info("Hardware aware grouping completed\n");
>                         return 0;
> +               }
>         }
>
>         return parse_groups(perf_evlist, pmu, str, metric_no_group, metric_no_merge,
> diff --git a/tools/perf/util/metricgroup.h b/tools/perf/util/metricgroup.h
> index 51596e4b4341..37fdf8c5ba77 100644
> --- a/tools/perf/util/metricgroup.h
> +++ b/tools/perf/util/metricgroup.h
> @@ -79,6 +79,21 @@ struct metric_expr {
>  #define TRANSFER_FIRST_BYTE(pos) (7 - pos)
>  #define TRANSFER_SEC_BYTE(pos) (23 - pos)
>
> +/* Special events that are not described in pmu-event JSON files.
> + * topdown-* and TSC use dedicated registers, set as free
> + * counter for grouping purpose
> + */
> +enum special_events {
> +       TOPDOWN = 0,
> +       TSC     = 1,
> +       SPECIAL_EVENT_MAX,
> +};
> +
> +static const char *const special_event_names[SPECIAL_EVENT_MAX] = {
> +       "topdown-",
> +       "TSC",
> +};
> +
>  /**
>   * An event used in a metric. This info is for metric grouping.
>   */
> --
> 2.39.3
>