From: Arnout Vandecappelle <arnout@mind.be>
To: Philippe Gerum <rpm@xenomai.org>
Cc: xenomai@xenomai.org
Subject: Re: [Xenomai] CPU occupation without context switches?
Date: Wed, 23 May 2012 10:31:17 +0200 [thread overview]
Message-ID: <4FBCA055.9060607@mind.be> (raw)
In-Reply-To: <4FBBECA0.4020502@xenomai.org>
On 05/22/12 21:44, Philippe Gerum wrote:
> On 05/22/2012 06:09 PM, Arnout Vandecappelle wrote:
>> Hoi,
>>
>> After a few minutes of running my application, I see this:
>>
>> # cat /proc/xenomai/stat
>> CPU PID MSW CSW PF STAT %CPU NAME
>> 1 828 22 65 0 00300182 9.8 bench_RTnet_scope_thread_loop
>> 1 839 2 46627538 0 00300186 53.8 bench_RTnet
>> ...
>>
>> i.e. the bench_RTnet_scope_thread_loop takes 10% CPU but no
>> context switches. How is this possible? I've looked at the
>> source code and can't find an explanation: when the exectime
>> accounting is updated, the csw is incremented as well (in
>> __xnpod_schedule()).
>>
>
> Unless your thread which seems to repeatedly attempt to pend on some sync object has its wait condition satisfied on
> entry to the syscall most of the time, which may cause __xnpod_schedule() to leave it running without incrementing the
> switch count.
It is indeed possible that my application does something like that. But
wouldn't the switch count be incremented every time the bench_RTnet thread
is executed? That thread runs at 20kHz and at higher priority so it should
pre-empt the other one, which should lead to context switches in the _loop
thread.
Unfortunately, I can't reproduce the situation anymore... If I can I'll
try with Xenomai 2.6.0.
Regards,
Arnout
--
Arnout Vandecappelle arnout at mind be
Senior Embedded Software Architect +32-16-286540
Essensium/Mind http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint: 7CB5 E4CC 6C2E EFD4 6E3D A754 F963 ECAB 2450 2F1F
next prev parent reply other threads:[~2012-05-23 8:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-22 16:09 [Xenomai] CPU occupation without context switches? Arnout Vandecappelle
2012-05-22 18:17 ` Gilles Chanteperdrix
2012-05-22 19:44 ` Philippe Gerum
2012-05-23 8:31 ` Arnout Vandecappelle [this message]
2012-05-23 8:45 ` Philippe Gerum
2012-05-23 9:37 ` Philippe Gerum
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