linux-kernel - Re: [PATCH] perf/test: fix perf ftrace test on s390

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Message-ID: <Zy0X9kz_tmjNue5D@google.com>
Date: Thu, 7 Nov 2024 11:41:42 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Thomas Richter <tmricht@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	acme@...nel.org, sumanthk@...ux.ibm.com, agordeev@...ux.ibm.com,
	gor@...ux.ibm.com, hca@...ux.ibm.com,
	Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH] perf/test: fix perf ftrace test on s390

On Thu, Nov 07, 2024 at 01:33:43PM +0100, Thomas Richter wrote:
> On s390 the perf test case ftrace sometimes fails as follows:
> 
>   # ./perf test ftrace
>   79: perf ftrace tests    : FAILED!
>   #
> 
> The failure depends on the kernel .config file. Some configurarions
> always work fine, some do not.

Which test do you fail?  ftrace trace or profile?  I don't think it's
gonna be a problem for ftrace latency.


> To achieve success for all our tested kernel configurations, enlarge
> the buffer to store the traces complete without wrapping.
> The default buffer size is too small  for all kernel configurations.
> Set the buffer size of /sys/kernel/tracing/buffer_size_kb to 16 MB

Actually you can use -m 16M option for perf ftrace trace and perf ftrace
profile.  Then you don't need to care about restoring the original size.

Thanks,
Namhyung

> 
> Output after:
>   # ./perf test ftrace
>   79: perf ftrace tests     : Ok
>   #
> 
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> Suggested-by: Sven Schnelle <svens@...ux.ibm.com>
> ---
>  tools/perf/tests/shell/ftrace.sh | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/tools/perf/tests/shell/ftrace.sh b/tools/perf/tests/shell/ftrace.sh
> index a6ee740f0d7e..742d6b8f34d3 100755
> --- a/tools/perf/tests/shell/ftrace.sh
> +++ b/tools/perf/tests/shell/ftrace.sh
> @@ -80,10 +80,21 @@ test_ftrace_profile() {
>      echo "perf ftrace profile test  [Success]"
>  }
>  
> +if [ "$(uname -m)" = "s390x" ]
> +then
> +	ftrace_size=$(cat /sys/kernel/tracing/buffer_size_kb)
> +	echo 16384 > /sys/kernel/tracing/buffer_size_kb
> +fi
> +
>  test_ftrace_list
>  test_ftrace_trace
>  test_ftrace_latency
>  test_ftrace_profile
>  
> +if [ "$(uname -m)" = "s390x" ]
> +then
> +	echo $ftrace_size > /sys/kernel/tracing/buffer_size_kb
> +fi
> +
>  cleanup
>  exit 0
> -- 
> 2.47.0
>