linux-kernel - Re: [PATCH] perf tests switch-tracking: Fix timestamp comparison

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Message-ID: <aDcK5arEEsccWsJC@x1>
Date: Wed, 28 May 2025 10:08:53 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Leo Yan <leo.yan@....com>
Cc: Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"Liang, Kan" <kan.liang@...ux.intel.com>,
	James Clark <james.clark@...aro.org>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf tests switch-tracking: Fix timestamp comparison

On Tue, May 27, 2025 at 10:49:24AM +0100, Leo Yan wrote:
> On Fri, May 23, 2025 at 02:12:58PM -0300, Arnaldo Carvalho de Melo wrote:
 
> [...]
 
> > Thanks for the extra info, I'll add it to the commit log message, and
> > perhaps we could make this test exclusive and use stress-ng to generate
> > some background noise in the form of a good number of processes, see:

> > root@x1:~# stress-ng --switch $(($(nproc) * 2)) --timeout 30s & for a in $(seq 50) ; do perf test switch ; done
 
> Thanks for sharing the test command.
> 
> > Now with your patch it also fails, so its for another reason:

> > --- start ---
> > test child forked, pid 1777071
> > Using CPUID GenuineIntel-6-BA-3
> > mmap size 528384B
> > 45221 events recorded
> > Missing comm events
> > ---- end(-1) ----
> > 113: Track with sched_switch                                         : FAILED!
> > 
> > Lots of short lived processes makes it fail as well :-\
 
> I searched internal CI record, we also occasionally saw the error:
 
>   Missing cycles events
 
> I will find time to check if anything in test can be improved.  Seems
> to me, the test is fragile if system has background activities.

Great!
 
> > Your patch is correct, so I'll probably just add your comments and go
> > with it.
 
> Thanks!  Also thanks Ian's suggestion for the iteration command.

You're welcome, thanks for your work on improving perf, really
appreciated!

- Arnaldo