linux-kernel - Re: [PATCH v2 2/2] perf stat: Stop repeating when ref_perf

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Message-ID: <39eafc82-dfa8-4e22-9d8a-071ed09460d3@linaro.org>
Date: Fri, 13 Sep 2024 09:36:54 +0100
From: James Clark <james.clark@...aro.org>
To: Levi Yun <yeoreum.yun@....com>
Cc: nd@....com, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org, 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,
 adrian.hunter@...el.com, asmadeus@...ewreck.org
Subject: Re: [PATCH v2 2/2] perf stat: Stop repeating when ref_perf_stat()
 returns -1



On 13/09/2024 03:02, 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>
> ---
> Changes in v2:
>    - Add some comments.
> ---
>   tools/perf/builtin-stat.c | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index 954eb37ce7b8..0153925f2382 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -2875,7 +2875,15 @@ 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) {
> +		/*
> +		 * * Meet COUNTER_FATAL situation (i.e) can't open event counter.
> +		 * * In this case, there is a high chance of failure in the next attempt
> +		 * * as well with the same reason. so, stop it.
> +		 * */

There's something wrong with the formatting here.

But I don't think the comment answers my question about the other return 
codes. It just states what the code does.

There are many more return -1's than just for COUNTER_FATAL, so it's not 
just that situation anyway. And in addition to that, there is -ENOMEM 
and others that aren't -1 which aren't explained that they are 
deliberately explicit retry or ignores.

> +		if (status == -1)
> +			break;
> +
> +		if (forever && !interval) {
>   			print_counters(NULL, argc, argv);
>   			perf_stat__reset_stats();
>   		}
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
>