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

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Date:	Sat, 20 Sep 2008 09:59:45 -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>,
	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:
> 
> > I thought we had a wakeup latency tracer exacty like we have preempt and
> > irq off latency tracers, Steve, where'd that go?
> 
> I rebuilt my kernel after a make clean and wakeup was still not there. It
> might be a good idea to modify the kernel documentation currently
> provided with 2.6.27 if it has gone away for now (or document the extra
> switches needed to turn it on if that's why it didn't show up for me)...

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.

-- Steve

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