Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761665AbXETCpo (ORCPT ); Sat, 19 May 2007 22:45:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758410AbXETCph (ORCPT ); Sat, 19 May 2007 22:45:37 -0400 Received: from homer.mvista.com ([63.81.120.158]:40256 "EHLO gateway-1237.mvista.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1757225AbXETCpg (ORCPT ); Sat, 19 May 2007 22:45:36 -0400 Subject: Re: [PATCH 2.6.21-rt2] PowerPC: decrementer clockevent driver From: Daniel Walker To: Paul Mackerras Cc: Sergei Shtylyov , linuxppc-dev@ozlabs.org, tglx@linutronix.de, mingo@elte.hu, linux-kernel@vger.kernel.org In-Reply-To: <17998.28659.702653.237011@cargo.ozlabs.ibm.com> References: <200705172142.26739.sshtylyov@ru.mvista.com> <8E44DB06-767D-4864-8D2C-6132E4D4370B@kernel.crashing.org> <464C99FF.8080404@ru.mvista.com> <135307ED-7125-4859-8594-4B5B900D92D6@kernel.crashing.org> <1179500217.20519.53.camel@imap.mvista.com> <464DC0DC.7050809@ru.mvista.com> <1179502773.20519.56.camel@imap.mvista.com> <17998.28659.702653.237011@cargo.ozlabs.ibm.com> Content-Type: text/plain Date: Sat, 19 May 2007 19:43:11 -0700 Message-Id: <1179628991.20925.2.camel@imap.mvista.com> Mime-Version: 1.0 X-Mailer: Evolution 2.8.3 (2.8.3-2.fc6) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1123 Lines: 27 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/