From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751353AbWDQWfV (ORCPT ); Mon, 17 Apr 2006 18:35:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751359AbWDQWfV (ORCPT ); Mon, 17 Apr 2006 18:35:21 -0400 Received: from mustang.oldcity.dca.net ([216.158.38.3]:45771 "HELO mustang.oldcity.dca.net") by vger.kernel.org with SMTP id S1751353AbWDQWfV (ORCPT ); Mon, 17 Apr 2006 18:35:21 -0400 Subject: Re: [-rt] time-related problems with CPU frequency scaling From: Lee Revell To: woho@woho.de Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner In-Reply-To: <200604162041.10844.woho@woho.de> References: <200604162041.10844.woho@woho.de> Content-Type: text/plain Date: Mon, 17 Apr 2006 18:35:16 -0400 Message-Id: <1145313317.16138.90.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.6.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org 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