Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764424AbYFKRAy (ORCPT ); Wed, 11 Jun 2008 13:00:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753502AbYFKRAq (ORCPT ); Wed, 11 Jun 2008 13:00:46 -0400 Received: from mx2.compro.net ([216.54.166.4]:2441 "EHLO mx2.compro.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751186AbYFKRAp (ORCPT ); Wed, 11 Jun 2008 13:00:45 -0400 X-IronPort-AV: E=Sophos;i="4.27,625,1204520400"; d="scan'208";a="2333408" Message-ID: <4850046C.4070602@compro.net> Date: Wed, 11 Jun 2008 12:59:24 -0400 From: Mark Hounschell Reply-To: markh@compro.net Organization: Compro Computer Svcs. User-Agent: Thunderbird 2.0.0.9 (X11/20070801) MIME-Version: 1.0 To: Arjan van de Ven CC: "linux-os (Dick Johnson)" , Jan Engelhardt , "Kok, Auke" , "solsTiCe d'Hiver" , linux-kernel@vger.kernel.org Subject: Re: PROBLEM: no cpu MHz in /proc/cpuinfo on 2.6.25.4-rt6 References: <200806102152.23286.solstice.dhiver@gmail.com> <20080610131314.5f7069e6@infradead.org> <484EE71A.40002@intel.com> <20080611063639.5e1eea5b@infradead.org> <20080611065816.6cff290d@infradead.org> <20080611083644.32afc823@infradead.org> In-Reply-To: <20080611083644.32afc823@infradead.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1535 Lines: 49 Arjan van de Ven wrote: > On Wed, 11 Jun 2008 10:14:50 -0400 > "linux-os (Dick Johnson)" wrote: > >> I use CPU frequency to scale the output of rdtsc when timing >> routines being optimized. > > Ok this is broken in various really bad ways. > > 1) CPU frequency is very fluctuating, it changes in principle every > millisecond or more I'm curious. What do you mean by "in principle"? And why will it change? > 2) the rdtsc "frequency" is conceptually unrelated to cpu frequency. In > fact, you'll be hard-pressed to buy a system today where this > relationship works.... > And what do you mean by "conceptually unrelated to cpu frequency"? Is it not the clock freq that is driving the cpu and the freq at which the tsc is incremented? > >> If CPU frequency goes away, I'll >> have to add calibration routines to a lot of code. I don't >> think one should just dispose of something that has been >> useful for many years because they don't understand its >> utility. > > clearly you don't understand it either ;-) > Could you explain what we don't understand about this please? > I'm not arguing for removing it, at all. I'm just arguing that any user > of it (being human or program) has some problems in how they use the > data. > > > Regards Mark -- 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/