linux-kernel - Re: [PATCH v1] perf stat: Avoid merging/aggregating metric counts twice

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Date:   Thu, 9 Feb 2023 11:06:22 -0800
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        James Clark <james.clark@....com>,
        Eduard Zingerman <eddyz87@...il.com>,
        Florian Fischer <florian.fischer@...q.space>,
        Zhengjun Xing <zhengjun.xing@...ux.intel.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Perry Taylor <perry.taylor@...el.com>
Subject: Re: [PATCH v1] perf stat: Avoid merging/aggregating metric counts twice

Hi Ian,

On Wed, Feb 8, 2023 at 10:45 PM Ian Rogers <irogers@...gle.com> wrote:
>
> The added perf_stat_merge_counters combines uncore counters. When
> metrics are enabled, the counts are merged into a metric_leader
> via the stat-shadow saved_value logic. As the leader now is
> passed an aggregated count, it leads to all counters being added
> together twice and counts appearing approximately doubled in
> metrics.
>
> This change disables the saved_value merging of counts for evsels
> that are merged. It is recommended that later changes remove the
> saved_value entirely as the two layers of aggregation in the code
> is confusing.

+1

>
> Fixes: 942c5593393d ("perf stat: Add perf_stat_merge_counters()")
> Reported-by: Perry Taylor <perry.taylor@...el.com>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung


> ---
>  tools/perf/util/stat-shadow.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
> index cadb2df23c87..4cd05d9205e3 100644
> --- a/tools/perf/util/stat-shadow.c
> +++ b/tools/perf/util/stat-shadow.c
> @@ -311,7 +311,7 @@ void perf_stat__update_shadow_stats(struct evsel *counter, u64 count,
>                 update_stats(&v->stats, count);
>                 if (counter->metric_leader)
>                         v->metric_total += count;
> -       } else if (counter->metric_leader) {
> +       } else if (counter->metric_leader && !counter->merged_stat) {
>                 v = saved_value_lookup(counter->metric_leader,
>                                        map_idx, true, STAT_NONE, 0, st, rsd.cgrp);
>                 v->metric_total += count;
> --
> 2.39.1.519.gcb327c4b5f-goog
>