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Date:	Sat, 19 May 2007 19:43:11 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Sergei Shtylyov <sshtylyov@...mvista.com>, linuxppc-dev@...abs.org,
	tglx@...utronix.de, mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver

On Sat, 2007-05-19 at 13:33 +1000, Paul Mackerras wrote: 
> Daniel Walker writes:
> 
> > On Fri, 2007-05-18 at 19:06 +0400, Sergei Shtylyov wrote:
> > >     Well, the decrementer frequency may change, at least in theory (if the bus 
> > > clock changes).
> > 
> > Does that happen very often?
> 
> If it did, gettimeofday would start reporting seriously wrong values,
> since the timebase and the decrementer count at the same rate, and we
> don't have any provision for fixing things up if that rate changed.
> Fortunately there are no powerpc platforms where the rate is
> variable.

In terms of clocksources, gettimeofday() would have to switch to another
clocksource if the decrementer started to act that way .. That's why it
is possible to register more than one clocksource, to allow for the
switching. The decrementer frequency doesn't change even with cpufreq?

Daniel

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