linux-kernel - Re: Reading EeePC900 battery info causes stalls (was Re: How how latent should non-preemptive scheduling be?)

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Message-ID: <alpine.DEB.1.10.0809201037070.13540@gandalf.stny.rr.com>
Date:	Sat, 20 Sep 2008 10:37:28 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sitsofe Wheeler <sitsofe@...oo.com>
cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>, lenb@...nel.org,
	astarikovskiy@...e.de
Subject: Re: Reading EeePC900 battery info causes stalls (was Re: How how  
 latent should non-preemptive scheduling be?)

On Sat, 20 Sep 2008, Sitsofe Wheeler wrote:

> Steven Rostedt wrote:
> > The wake up tracing is CONFIG_SCHED_TRACER. If you do not see "wakeup" as
> > one of the available tracers in available_tracers, then check
> > your dmesg and see if you have CONFIG_FTRACE_STARTUP_TEST enabled. There was
> > a known bug that would cause the wakeup tracing to fail the test. When a
> > trace fails the startup test, it is disabled.
> 
> This is exactly the case (dmesg reports the ftrace wakeup startup test
> failed). That's what I get for not reading my dmesg more carefully...

OK, that is probably the known bug you are hitting. Simply disable the 
CONFIG_FTRACE_STARTUP_TEST and you should have the wakeup tracer. The bug 
is with the test, not the tracer, so it should not hurt you.

-- Steve

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