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

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Message-ID: <ae0f7492-412b-4506-9127-514577b33e7e@linux.ibm.com>
Date: Thu, 14 Nov 2024 16:34:06 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: James Clark <james.clark@...aro.org>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org, namhyung@...nel.org,
        svens@...ux.ibm.com
Cc: agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com
Subject: Re: [PING PATCH] perf/test: fix perf ftrace test on s390

On 11/14/24 12:09, James Clark wrote:
> 
> 
> On 14/11/2024 9:01 am, 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.  The ftrace profile test mostly fails,
>> because the ring buffer was not large enough, and some lines
>> (especially the interesting ones with nanosleep in it) where dropped.
>>
>> 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
>>
>>
>> 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
>> +
> 
> It probably wouldn't be terrible to do this for all platforms to reduce fragmentation. It doesn't do any harm and it only added a few seconds to the test time even on a small Arm box, maybe it will prevent flakes everywhere else in the future. But I don't feel too strongly about this one.
> 
>>   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
>> +
> 
> Restoring the value should be in cleanup() so it works on interrupt too.
> 
> With that:
> 
> Reviewed-by: James Clark <james.clark@...aro.org>
> 

Thanks for your feedback. Will do it and post v2

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

Vorsitzender des Aufsichtsrats: Wolfgang Wendt

Geschäftsführung: David Faller

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