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

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Message-ID: <yt9diksyqlx6.fsf@linux.ibm.com>
Date: Fri, 08 Nov 2024 07:28:21 +0100
From: Sven Schnelle <svens@...ux.ibm.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Thomas Richter <tmricht@...ux.ibm.com>, 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
Subject: Re: [PATCH] perf/test: fix perf ftrace test on s390

Namhyung Kim <namhyung@...nel.org> writes:

> 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.


The ftrace profile test failed, 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
>
> 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.

Ok, thanks. I leave it to Thomas to decide whether he wants to add this
option to the CI run.

Thanks!