linux-kernel - Re: [PATCH] perf stat: Fix shadow stats for clock events

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Date:   Fri, 16 Nov 2018 14:35:55 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        namhyung@...nel.org, yao.jin@...ux.intel.com,
        linux-kernel@...r.kernel.org, yuzhoujian@...ichuxing.com,
        tmricht@...ux.vnet.ibm.com, anton@...ba.org
Subject: Re: [PATCH] perf stat: Fix shadow stats for clock events

On Fri, Nov 16, 2018 at 09:58:43AM +0530, Ravi Bangoria wrote:
> Commit 0aa802a79469 ("perf stat: Get rid of extra clock display
> function") introduced scale and unit for clock events. Thus,
> perf_stat__update_shadow_stats() now saves scaled values of
> clock events in msecs, instead of original nsecs. But while
> calculating values of shadow stats we still consider clock
> event values in nsecs. This results in a wrong shadow stat
> values. Ex,
> 
>   # ./perf stat -e task-clock,cycles ls
>     <SNIP>
>               2.60 msec task-clock:u    #    0.877 CPUs utilized
>          2,430,564      cycles:u        # 1215282.000 GHz
> 
> Fix this by saving original nsec values for clock events in
> perf_stat__update_shadow_stats(). After patch:
> 
>   # ./perf stat -e task-clock,cycles ls
>     <SNIP>
>               3.14 msec task-clock:u    #    0.839 CPUs utilized
>          3,094,528      cycles:u        #    0.985 GHz
> 
> Reported-by: Anton Blanchard <anton@...ba.org>
> Suggested-by: Jiri Olsa <jolsa@...hat.com>
> Fixes: 0aa802a79469 ("perf stat: Get rid of extra clock display function")
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.ibm.com>

Reviewed-by: Jiri Olsa <jolsa@...nel.org>

thanks,
jirka

> ---
>  tools/perf/util/stat-shadow.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
> index f0a8cec55c47..3c22c58b3e90 100644
> --- a/tools/perf/util/stat-shadow.c
> +++ b/tools/perf/util/stat-shadow.c
> @@ -209,11 +209,12 @@ void perf_stat__update_shadow_stats(struct perf_evsel *counter, u64 count,
>  				    int cpu, struct runtime_stat *st)
>  {
>  	int ctx = evsel_context(counter);
> +	u64 count_ns = count;
>  
>  	count *= counter->scale;
>  
>  	if (perf_evsel__is_clock(counter))
> -		update_runtime_stat(st, STAT_NSECS, 0, cpu, count);
> +		update_runtime_stat(st, STAT_NSECS, 0, cpu, count_ns);
>  	else if (perf_evsel__match(counter, HARDWARE, HW_CPU_CYCLES))
>  		update_runtime_stat(st, STAT_CYCLES, ctx, cpu, count);
>  	else if (perf_stat_evsel__is(counter, CYCLES_IN_TX))
> -- 
> 2.17.1
>