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From: Wolfgang Hoffmann <woho@woho.de>
Reply-To: woho@woho.de
To: linux-kernel@vger.kernel.org
Subject: Re: [-rt] time-related problems with CPU frequency scaling
Date: Thu, 20 Apr 2006 20:39:30 +0200
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Cc: Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
       Lee Revell <rlrevell@joe-job.com>
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On Sunday 16 April 2006 20:41, Wolfgang Hoffmann wrote:
> Now with speedstep enabled and CONFIG_HIGH_RES_TIMERS=y, I see some
> anomalies:
> - time-of-day lags gradually behind wallclock time

It turns out that this is a non-issue. I can't quite explain how I came to the 
impression that there is a clock lag, but current status is that the clock 
runs correctly. So sorry for the noise.

On Tuesday 18 April 2006 00:35, Lee Revell wrote:
> On Sun, 2006-04-16 at 20:41 +0200, Wolfgang Hoffmann wrote:
> > - if CPU frequency is low when jackd is started, it complains:
> >     "delay of 2915.000 usecs exceeds estimated spare
> >     time of 2847.000; restart ..."
> >   as soon as frequency is scaled up. Seems that jackd gets confused by
> > some influence of CPU frequency on timekeeping? No problems as long as
> > CPU frequency isn't scaled up, though.
>
> JACK still uses the TSC for timing and thus is incompatible with CPU
> frequency scaling.  You must use the -clockfix branch from CVS.

Thanks for the pointer, Lee. I'm now running the clockfix CVS branch and the 
problems are solved. So the -rt kernel is fine.

Thanks for the help,
Wolfgang