linux-kernel - Re: [PATCH] perf test: Remove atomics from test

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Message-ID: <9e3355e0-f0d6-5f82-d2f6-b7e84bda996c@arm.com>
Date:   Fri, 3 Nov 2023 09:14:45 +0000
From:   James Clark <james.clark@....com>
To:     Nick Forrington <nick.forrington@....com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH] perf test: Remove atomics from test_loop to avoid test
 failures



On 02/11/2023 16:22, Nick Forrington wrote:
> The current use of atomics can lead to test failures, as tests (such as
> tests/shell/record.sh) search for samples with "test_loop" as the
> top-most stack frame, but find frames related to the atomic operation
> (e.g. __aarch64_ldadd4_relax).
> 
> This change simply removes the "count" variable, as it is not necessary.
> 
> Fixes: 1962ab6f6e0b ("perf test workload thloop: Make count increments atomic")
> Signed-off-by: Nick Forrington <nick.forrington@....com>
> ---
>   tools/perf/tests/workloads/thloop.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/tools/perf/tests/workloads/thloop.c b/tools/perf/tests/workloads/thloop.c
> index af05269c2eb8..457b29f91c3e 100644
> --- a/tools/perf/tests/workloads/thloop.c
> +++ b/tools/perf/tests/workloads/thloop.c
> @@ -7,7 +7,6 @@
>   #include "../tests.h"
>   
>   static volatile sig_atomic_t done;
> -static volatile unsigned count;
>   
>   /* We want to check this symbol in perf report */
>   noinline void test_loop(void);
> @@ -19,8 +18,7 @@ static void sighandler(int sig __maybe_unused)
>   
>   noinline void test_loop(void)
>   {
> -	while (!done)
> -		__atomic_fetch_add(&count, 1, __ATOMIC_RELAXED);
> +	while (!done);
>   }
>   
>   static void *thfunc(void *arg)

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