From owner-freebsd-arch@FreeBSD.ORG Wed Mar 19 06:44:36 2008 Return-Path: Delivered-To: arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 94A9B106564A for ; Wed, 19 Mar 2008 06:44:36 +0000 (UTC) (envelope-from peterjeremy@optushome.com.au) Received: from mail15.syd.optusnet.com.au (mail15.syd.optusnet.com.au [211.29.132.196]) by mx1.freebsd.org (Postfix) with ESMTP id 12B398FC22 for ; Wed, 19 Mar 2008 06:44:35 +0000 (UTC) (envelope-from peterjeremy@optushome.com.au) Received: from server.vk2pj.dyndns.org (c220-239-20-82.belrs4.nsw.optusnet.com.au [220.239.20.82]) by mail15.syd.optusnet.com.au (8.13.1/8.13.1) with ESMTP id m2J6iXBL002633 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 19 Mar 2008 17:44:34 +1100 Received: from server.vk2pj.dyndns.org (localhost.vk2pj.dyndns.org [127.0.0.1]) by server.vk2pj.dyndns.org (8.14.2/8.14.1) with ESMTP id m2J6iXlQ072441; Wed, 19 Mar 2008 17:44:33 +1100 (EST) (envelope-from peter@server.vk2pj.dyndns.org) Received: (from peter@localhost) by server.vk2pj.dyndns.org (8.14.2/8.14.2/Submit) id m2J6iXM9072440; Wed, 19 Mar 2008 17:44:33 +1100 (EST) (envelope-from peter) Date: Wed, 19 Mar 2008 17:44:33 +1100 From: Peter Jeremy To: Poul-Henning Kamp Message-ID: <20080319064433.GA44676@server.vk2pj.dyndns.org> References: <20080318182358.F34016@fledge.watson.org> <1278.1205869922@critter.freebsd.dk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="YZVh52eu0Ophig4D" Content-Disposition: inline In-Reply-To: <1278.1205869922@critter.freebsd.dk> X-PGP-Key: http://members.optusnet.com.au/peterjeremy/pubkey.asc User-Agent: Mutt/1.5.17 (2007-11-01) Cc: arch@freebsd.org Subject: Re: Power-Mgt (Was: Re: cvs commit: src/sys/i386/cpufreq est.c ) X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Mar 2008 06:44:36 -0000 --YZVh52eu0Ophig4D Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Mar 18, 2008 at 07:52:02PM +0000, Poul-Henning Kamp wrote: >When we talk about macroscopic efforts, turning of hardware we don't >use, spinning down disks, common sense says that power is saved and >we can leave it at that. Except that it takes more power to spin up a disk than keep is spinning. Even neglecting the disk life issue, powering a disk down for a short period and then powering it back up may use more energy than keeping it running. >I have not tried to find out how exact the power measurements ACPI >offers on laptops are, I know some of the chips used but have >never double-checked the result. I don't believe ACPI lets you get at the numbers with sufficient resolution to manage anything particularly meaningful. In any case, repeatability and monotonicity are more of an issue than absolute accuracy: As long as we can meaningfully do relational comparisons then we can make progress. I suspect the results are going to vary significantly between systems anyway. >affect the results), but few off them allow you to measure power >(ie: Watts) without hooking up GPIB and accumulating a lot of >current measurements by hand. Any decent bench supply should be stiff enough to treat the voltage as a constant so just monitoring the current is adequate to calculate power. If you want to monitor energy then, yes you probably need to hook it up to an external logger. You can buy a multimeter with a USB interface for AUD140 (