linux-kernel - Re: [PATCH v3 2/2] perf stat: Stop repeating when ref_perf

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Message-ID: <d6df6edd-688d-403d-8006-491e302fd042@linaro.org>
Date: Fri, 13 Sep 2024 14:49:24 +0100
From: James Clark <james.clark@...aro.org>
To: Levi Yun <yeoreum.yun@....com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 nd@....com, peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
 namhyung@...nel.org, mark.rutland@....com,
 alexander.shishkin@...ux.intel.com, jolsa@...nel.org, irogers@...gle.com,
 asmadeus@...ewreck.org
Subject: Re: [PATCH v3 2/2] perf stat: Stop repeating when ref_perf_stat()
 returns -1



On 13/09/2024 11:14, Levi Yun wrote:
> Exit when run_perf_stat() returns an error to avoid continuously
> repeating the same error message. It's not expected that COUNTER_FATAL
> or internal errors are recoverable so there's no point in retrying.
> 
> This fixes the following flood of error messages for permission issues,
> for example when perf_event_paranoid==3:
>    perf stat -r 1044 -- false
> 
>    Error:
>    Access to performance monitoring and observability operations is limited.
>    ...
>    Error:
>    Access to performance monitoring and observability operations is limited.
>    ...
>    (repeating for 1044 times).
> 
> Signed-off-by: Levi Yun <yeoreum.yun@....com>
> ---
>   tools/perf/builtin-stat.c | 14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 954eb37ce7b8..d25528ea7e40 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -2875,7 +2875,19 @@ int cmd_stat(int argc, const char **argv)
>   			evlist__reset_prev_raw_counts(evsel_list);
>   
>   		status = run_perf_stat(argc, argv, run_idx);
> -		if (forever && status != -1 && !interval) {
> +
> +		/*
> +		 * Returns -1 for fatal errors which signifies to not continue
> +		 * when in repeat mode.
> +		 *
> +		 * Returns < -1 error codes when stat record is used. These
> +		 * result in the stat information being displayed, but writing
> +		 * to the file fails and is non fatal.
> +		 */

I meant this to be a function doc above the run_perf_stat() function. 
Usually what a function returns would be documented there, in case there 
end up being multiple callers.

With that change:

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

Also I think something happened with the cover letter as well, it's 
marked as V2.