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

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Message-ID: <20250527094924.GF2566836@e132581.arm.com>
Date: Tue, 27 May 2025 10:49:24 +0100
From: Leo Yan <leo.yan@....com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
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 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.

> 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.

Leo