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From: Ingo Molnar <mingo@elte.hu>
To: Frans Pop <elendil@planet.nl>
Cc: linux-kernel@vger.kernel.org,
	Dhaval Giani <dhaval@linux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@sisk.pl>,
	Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [rc8] Regression: key repeats and skips in music during compilation
Date: Tue, 8 Apr 2008 15:54:00 +0200	[thread overview]
Message-ID: <20080408135400.GA18493@elte.hu> (raw)
In-Reply-To: <200804081137.20063.elendil@planet.nl>


* Frans Pop <elendil@planet.nl> wrote:

> > and a more laborous way would be to trace such skipping:
> >  http://people.redhat.com/mingo/sched-devel.git/howto-trace-latencies.txt
> 
> Tried this too, but the problem is that the skips don't happen while 
> tracing is enabled. Apparently the system overhead is so high that it 
> changes the scheduling behavior. Attached one trace that was made 
> immediately after a skip happened. Maybe it helps.

one way to reduce tracing overhead would be:

  echo nostacktrace > /sys/kernel/debug/tracing/iter_ctrl
  echo nosched-tree > /sys/kernel/debug/tracing/iter_ctrl

and making sure you only have CONFIG_CONTEXT_SWITCH_TRACER=y enabled, 
not any of the other tracers.

but ... if there's a narrow wakeup race, even lightweight tracing could 
make it go away.

	Ingo



  parent reply	other threads:[~2008-04-08 13:54 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-04-04 10:22 Frans Pop
2008-04-06 20:39 ` Rafael J. Wysocki
2008-04-07  9:21   ` Rafael J. Wysocki
2008-04-07 10:05     ` Frans Pop
2008-04-07 10:29       ` Rafael J. Wysocki
2008-04-07 11:24         ` Dhaval Giani
2008-04-07 12:03           ` Frans Pop
2008-04-07 12:25             ` Peter Zijlstra
2008-04-07 21:55               ` Frans Pop
2008-04-07 12:32             ` Ingo Molnar
     [not found]               ` <200804081137.20063.elendil@planet.nl>
2008-04-08 13:54                 ` Ingo Molnar [this message]
2008-04-12 11:29             ` Richard Jonsson
2008-04-19 21:31               ` Richard Jonsson
2008-04-19 22:05                 ` Frans Pop
2008-04-21 14:16                   ` Richard Jonsson

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