From owner-freebsd-current@FreeBSD.ORG Mon Oct 31 15:20:46 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 C224616A41F; Mon, 31 Oct 2005 15:20:46 +0000 (GMT) (envelope-from obrien@NUXI.com) Received: from dragon.NUXI.org (trang.nuxi.com [66.93.134.19]) by mx1.FreeBSD.org (Postfix) with ESMTP id 3DFE743D45; Mon, 31 Oct 2005 15:20:46 +0000 (GMT) (envelope-from obrien@NUXI.com) Received: from dragon.NUXI.org (obrien@localhost [127.0.0.1]) by dragon.NUXI.org (8.13.4/8.13.4) with ESMTP id j9VFKjwr019540; Mon, 31 Oct 2005 07:20:45 -0800 (PST) (envelope-from obrien@dragon.NUXI.org) Received: (from obrien@localhost) by dragon.NUXI.org (8.13.4/8.13.1/Submit) id j9VFKiLb019539; Mon, 31 Oct 2005 07:20:44 -0800 (PST) (envelope-from obrien) Date: Mon, 31 Oct 2005 07:20:43 -0800 From: "David O'Brien" To: Robert Watson Message-ID: <20051031152043.GA19167@dragon.NUXI.org> Mail-Followup-To: freebsd-current@freebsd.org, Robert Watson , Alexander Leidinger , David Xu 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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20051031083447.Y11619@fledge.watson.org> X-Operating-System: FreeBSD 7.0-CURRENT Organization: The NUXI BSD Group X-Pgp-Rsa-Fingerprint: B7 4D 3E E9 11 39 5F A3 90 76 5D 69 58 D9 98 7A X-Pgp-Rsa-Keyid: 1024/34F9F9D5 User-Agent: Mutt/1.5.9i Cc: Alexander Leidinger , freebsd-current@FreeBSD.org, David Xu 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 Reply-To: freebsd-current@FreeBSD.org 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 15:20:46 -0000 On Mon, Oct 31, 2005 at 09:26:11AM +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. Setting sysctl kern.timecounter.hardware=tsc isn't a great idea. PHK has mentioned several times how it seems many are wanting to play it fast and loose with the time source to the kernel. Providing some alternate loose time answers to an application such as MySQL that doesn't need accurate timing and presumable can handle variation would be a good thing. But that is different than simply setting kern.timecounter.hardware=tsc -- -- David (obrien@FreeBSD.org)