From owner-freebsd-current@FreeBSD.ORG Fri Oct 28 13:47:29 2005 Return-Path: X-Original-To: current@freebsd.org Delivered-To: freebsd-current@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id C014316A420 for ; Fri, 28 Oct 2005 13:47:29 +0000 (GMT) (envelope-from cperciva@freebsd.org) Received: from pd3mo3so.prod.shaw.ca (shawidc-mo1.cg.shawcable.net [24.71.223.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id 6369C43D48 for ; Fri, 28 Oct 2005 13:47:29 +0000 (GMT) (envelope-from cperciva@freebsd.org) Received: from pd4mr3so.prod.shaw.ca (pd4mr3so-qfe3.prod.shaw.ca [10.0.141.214]) by l-daemon (Sun ONE Messaging Server 6.0 HotFix 1.01 (built Mar 15 2004)) with ESMTP id <0IP2005KUOZ4R5B0@l-daemon> for current@freebsd.org; Fri, 28 Oct 2005 07:47:28 -0600 (MDT) Received: from pn2ml9so.prod.shaw.ca ([10.0.121.7]) by pd4mr3so.prod.shaw.ca (Sun ONE Messaging Server 6.0 HotFix 1.01 (built Mar 15 2004)) with ESMTP id <0IP2006AAOZ4U350@pd4mr3so.prod.shaw.ca> for current@freebsd.org; Fri, 28 Oct 2005 07:47:28 -0600 (MDT) Received: from [192.168.0.60] (S0106006067227a4a.vc.shawcable.net [24.87.209.6]) by l-daemon (iPlanet Messaging Server 5.2 HotFix 1.18 (built Jul 28 2003)) with ESMTP id <0IP200N2YOZ42W@l-daemon> for current@freebsd.org; Fri, 28 Oct 2005 07:47:28 -0600 (MDT) Date: Fri, 28 Oct 2005 06:47:27 -0700 From: Colin Percival In-reply-to: <20051028153457.d0wqgn2ask4sgw4k@netchild.homeip.net> To: Alexander Leidinger Message-id: <43622BEF.3030006@freebsd.org> MIME-version: 1.0 Content-type: text/plain; charset=UTF-8 Content-transfer-encoding: 7bit X-Accept-Language: en-us, en X-Enigmail-Version: 0.92.1.0 References: <30595.1130493297@critter.freebsd.dk> <20051028153457.d0wqgn2ask4sgw4k@netchild.homeip.net> User-Agent: Mozilla Thunderbird 1.0.7 (X11/20051001) Cc: Poul-Henning Kamp , current@freebsd.org Subject: Re: TSC instead of ACPI: powerd doesn't work anymore (to be expected?) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 28 Oct 2005 13:47:29 -0000 Alexander Leidinger wrote: > Poul-Henning Kamp wrote: >> In general, if you run powerd to change your cpu clock (= TSC >> frequency), using TSC as timecounter is _not_ what you want to do. > > Is it not possible to recalibrate on frequency change, or is it "just" that > nobody wrote the code do to it? It's not possible in any useful way. When power management code changes the TSC frequency, it doesn't change the frequency directly; instead, it sends a message to the CPU saying "please, if you feel like it, could you change your frequency to some time soon?" Even if you manage to handle the change in frequency, the timecounter would significantly lose accuracy due to not knowing exactly when the change in frequency occurred. Colin Percival