From: Lee Revell <rlrevell@joe-job.com>
To: woho@woho.de
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [-rt] time-related problems with CPU frequency scaling
Date: Mon, 17 Apr 2006 18:35:16 -0400 [thread overview]
Message-ID: <1145313317.16138.90.camel@mindpipe> (raw)
In-Reply-To: <200604162041.10844.woho@woho.de>
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.
> - values in /proc/sys/kernel/preempt_max_latency scales inverse to
> CPU frequency, i.e. 24us with CPU @ 800MHz and 12us with CPU @ 1,6GHz
This is normal - code that takes 12us to run at 1.6 GHz will take 24us
at 800MHz. TANSTAAFL ;-)
Lee
next prev parent reply other threads:[~2006-04-17 22:35 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-04-16 18:41 [-rt] time-related problems with CPU frequency scaling Wolfgang Hoffmann
2006-04-17 22:35 ` Lee Revell [this message]
2006-04-18 6:11 ` Wolfgang Hoffmann
2006-04-18 6:32 ` Lee Revell
2006-04-20 18:39 ` Wolfgang Hoffmann
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