linux-kernel - Re: [PATCH 1/1] perf test task_exit: No need for a cycles event to check if we get an PERF_RECORD

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Message-ID: <ZLGXmMuNRpx1ubFm@kernel.org>
Date:   Fri, 14 Jul 2023 15:44:40 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] perf test task_exit: No need for a cycles event to
 check if we get an PERF_RECORD_EXIT

Forgot to CC lkml :-\

Em Fri, Jul 14, 2023 at 03:39:22PM -0300, Arnaldo Carvalho de Melo escreveu:
> The intent of this test is to check we get a PERF_RECORD_EXIT as asked
> for by setting perf_event_attr.task=1.
> 
> When the test was written we didn't have the "dummy" event so we went
> with the default event, "cycles".
> 
> There were reports of this test failing sometimes, one of these reports
> was with a PREEMPT_RT_FULL kernel, but I noticed it failing sometimes
> on an aarch64 Firefly board.
> 
> In the kernel the call to perf_event_task_output(), that generates the
> PERF_RECORD_EXIT may fail when there is not enough memory in the ring
> buffer, if the ring buffer is paused, etc.
> 
> So switch to using the "dummy" event to use the ring buffer just for
> what the test was designed for, avoiding uneeded PERF_RECORD_SAMPLEs.
> 
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/tests/task-exit.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/tests/task-exit.c b/tools/perf/tests/task-exit.c
> index 25f075fa9125bd53..968dddde6ddaf0be 100644
> --- a/tools/perf/tests/task-exit.c
> +++ b/tools/perf/tests/task-exit.c
> @@ -58,9 +58,9 @@ static int test__task_exit(struct test_suite *test __maybe_unused, int subtest _
>  
>  	signal(SIGCHLD, sig_handler);
>  
> -	evlist = evlist__new_default();
> +	evlist = evlist__new_dummy();
>  	if (evlist == NULL) {
> -		pr_debug("evlist__new_default\n");
> +		pr_debug("evlist__new_dummy\n");
>  		return -1;
>  	}
>  
> -- 
> 2.37.1
> 

-- 

- Arnaldo