linux-kernel - Re: [PATCH] perf stat: Use proper cpu for shadow stats

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Message-ID: <20201113221601.GE842058@krava>
Date:   Fri, 13 Nov 2020 23:16:01 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>, Sam Xi <xyzsam@...gle.com>
Subject: Re: [PATCH] perf stat: Use proper cpu for shadow stats

On Fri, Nov 13, 2020 at 02:02:36PM +0900, Namhyung Kim wrote:
> Currently perf stat shows some metrics (like IPC) for defined events.
> But when no aggregation mode is used (-A option), it shows incorrect
> values since it used a value from a different cpu.
> 
> Before:
> 
>   $ perf stat -aA -e cycles,instructions sleep 1
> 
>    Performance counter stats for 'system wide':
> 
>   CPU0      116,057,380      cycles
>   CPU1       86,084,722      cycles
>   CPU2       99,423,125      cycles
>   CPU3       98,272,994      cycles
>   CPU0       53,369,217      instructions      #    0.46  insn per cycle
>   CPU1       33,378,058      instructions      #    0.29  insn per cycle
>   CPU2       58,150,086      instructions      #    0.50  insn per cycle
>   CPU3       40,029,703      instructions      #    0.34  insn per cycle
> 
>        1.001816971 seconds time elapsed
> 
> So the IPC for CPU1 should be 0.38 (= 33,378,058 / 86,084,722)
> but it was 0.29 (= 33,378,058 / 116,057,380) and so on.
> 
> After:
> 
>   $ perf stat -aA -e cycles,instructions sleep 1
> 
>    Performance counter stats for 'system wide':
> 
>   CPU0      109,621,384      cycles
>   CPU1      159,026,454      cycles
>   CPU2       99,460,366      cycles
>   CPU3      124,144,142      cycles
>   CPU0       44,396,706      instructions      #    0.41  insn per cycle
>   CPU1      120,195,425      instructions      #    0.76  insn per cycle
>   CPU2       44,763,978      instructions      #    0.45  insn per cycle
>   CPU3       69,049,079      instructions      #    0.56  insn per cycle
> 
>        1.001910444 seconds time elapsed
> 
> Reported-by: Sam Xi <xyzsam@...gle.com>
> Fixes: 44d49a600259 ("perf stat: Support metrics in --per-core/socket mode")
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>

nice catch! would be great to have test for this

Acked-by: Jiri Olsa <jolsa@...hat.com>

thanks,
jirka

> ---
>  tools/perf/util/stat-display.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> index 4b57c0c07632..a963b5b8eb72 100644
> --- a/tools/perf/util/stat-display.c
> +++ b/tools/perf/util/stat-display.c
> @@ -324,13 +324,10 @@ static int first_shadow_cpu(struct perf_stat_config *config,
>  	struct evlist *evlist = evsel->evlist;
>  	int i;
>  
> -	if (!config->aggr_get_id)
> -		return 0;
> -
>  	if (config->aggr_mode == AGGR_NONE)
>  		return id;
>  
> -	if (config->aggr_mode == AGGR_GLOBAL)
> +	if (!config->aggr_get_id)
>  		return 0;
>  
>  	for (i = 0; i < evsel__nr_cpus(evsel); i++) {
> -- 
> 2.29.2.299.gdc1121823c-goog
>