Re: [PATCH v1] perf tool_pmu: Fix aggregation on duration_time

[James Clark <james.clark@linaro.org>]

On 23/04/2025 6:03 am, Ian Rogers wrote:
> evsel__count_has_error fails counters when the enabled or running time
> are 0. The duration_time event reads 0 when the cpu_map_idx != 0 to
> avoid aggregating time over CPUs. Change the enable and running time
> to always have a ratio of 100% so that evsel__count_has_error won't
> fail.
> 
> Before:
> ```
> $ sudo /tmp/perf/perf stat --per-core -a -M UNCORE_FREQ sleep 1
> 
>   Performance counter stats for 'system wide':
> 
> S0-D0-C0              1      2,615,819,485      UNC_CLOCK.SOCKET                 #     2.61 UNCORE_FREQ
> S0-D0-C0              2      <not counted>      duration_time
> 
>         1.002111784 seconds time elapsed
> ```
> 
> After:
> ```
> $ perf stat --per-core -a -M UNCORE_FREQ sleep 1
> 
>   Performance counter stats for 'system wide':
> 
> S0-D0-C0              1        758,160,296      UNC_CLOCK.SOCKET                 #     0.76 UNCORE_FREQ
> S0-D0-C0              2      1,003,438,246      duration_time
> 
>         1.002486017 seconds time elapsed
> ```
> 
> Note: the metric reads the value a different way and isn't impacted.
> 
> Reported-by: Stephane Eranian <eranian@google.com>
> Fixes: 240505b2d0ad ("perf tool_pmu: Factor tool events into their own PMU")
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>   tools/perf/util/tool_pmu.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/tool_pmu.c b/tools/perf/util/tool_pmu.c
> index 97b327d1ce4a..727a10e3f990 100644
> --- a/tools/perf/util/tool_pmu.c
> +++ b/tools/perf/util/tool_pmu.c
> @@ -486,8 +486,14 @@ int evsel__tool_pmu_read(struct evsel *evsel, int cpu_map_idx, int thread)
>   		delta_start *= 1000000000 / ticks_per_sec;
>   	}
>   	count->val    = delta_start;
> -	count->ena    = count->run = delta_start;
>   	count->lost   = 0;
> +	/*
> +	 * The values of enabled and running must make a ratio of 100%. The
> +	 * exact values don't matter as long as they are non-zero to avoid
> +	 * issues with evsel__count_has_error.
> +	 */
> +	count->ena++;
> +	count->run++;
>   	return 0;
>   }
>   

Reviewed-by: James Clark <james.clark@linaro.org>