From owner-freebsd-current@FreeBSD.ORG Mon Oct 31 13:29:57 2005 Return-Path: X-Original-To: freebsd-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 AFD3F16A41F; Mon, 31 Oct 2005 13:29:57 +0000 (GMT) (envelope-from scottl@samsco.org) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.FreeBSD.org (Postfix) with ESMTP id 91CAC43D7D; Mon, 31 Oct 2005 13:29:45 +0000 (GMT) (envelope-from scottl@samsco.org) Received: from [192.168.254.11] (junior.samsco.home [192.168.254.11]) (authenticated bits=0) by pooker.samsco.org (8.13.4/8.13.4) with ESMTP id j9VDTiSs027235; Mon, 31 Oct 2005 06:29:44 -0700 (MST) (envelope-from scottl@samsco.org) Message-ID: <43661C49.6090802@samsco.org> Date: Mon, 31 Oct 2005 06:29:45 -0700 From: Scott Long User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; en-US; rv:1.7.8) Gecko/20050615 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Robert Watson References: <30595.1130493297@critter.freebsd.dk> <20051028153457.d0wqgn2ask4sgw4k@netchild.homeip.net> <20051029195703.GB39253@dragon.NUXI.org> <43646AAC.2080107@freebsd.org> <20051030093718.GE39253@dragon.NUXI.org> <4364D90F.3090205@samsco.org> <20051031075843.GF39253@dragon.NUXI.org> <20051031083447.Y11619@fledge.watson.org> In-Reply-To: <20051031083447.Y11619@fledge.watson.org> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-1.4 required=3.8 tests=ALL_TRUSTED autolearn=failed version=3.1.0 X-Spam-Checker-Version: SpamAssassin 3.1.0 (2005-09-13) on pooker.samsco.org Cc: freebsd-current@FreeBSD.org, David O'Brien 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: Mon, 31 Oct 2005 13:29:57 -0000 Robert Watson wrote: > > On Sun, 30 Oct 2005, David O'Brien wrote: > >>> ACPI-fast requires an ioport read which takes about 1us (according to >>> Google). Do that 1000 times a second and you have each CPU spending >>> 1% of its time doing nothing but reading the clock. Yikes. >> >> >> But we've lived with using the ACPI timercounter (vs. TSC) for quite a >> while now. Why all of a sudden are the authors of this thread having >> an issue with it now. I know about the recent MySQL thread - but with >> the TSC being untrustable on MP and power managed systems, why is >> there such a desire to use the TSC? > > > Because in the past few weeks, several developers have noticed that if > you change timercounters from ACPI-fast to TSC, you get significant > performance boosts on real-world workloads. Drew reported this a couple > of weeks ago on net@ after looking at loopback network performance, and > I suggested he frob the timecounter on his system, which resulted in a > significant measured performance increase. Then recently it was > reported that MySQL also saw a significant boost from faster > timekeeping, as it performs frequent time measurement. > [...] Another thing to keep in mind is that now is an excellent time to start thinking about 7.0 and experimenting and validating possible improvements. Maybe we'll come to the conclusion that the TSC still isn't appropriate to use, or is only appropriate for certain scenarios, but unless we work with it now, we'll never know. Scott