From owner-freebsd-arch@FreeBSD.ORG Wed Mar 19 12:19:33 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 5623F1065672 for ; Wed, 19 Mar 2008 12:19:33 +0000 (UTC) (envelope-from phk@critter.freebsd.dk) Received: from phk.freebsd.dk (phk.freebsd.dk [130.225.244.222]) by mx1.freebsd.org (Postfix) with ESMTP id 1C28C8FC1A for ; Wed, 19 Mar 2008 12:19:32 +0000 (UTC) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (unknown [192.168.64.3]) by phk.freebsd.dk (Postfix) with ESMTP id DD56817104; Wed, 19 Mar 2008 12:19:30 +0000 (UTC) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.14.2/8.14.2) with ESMTP id m2JCJT4u009665; Wed, 19 Mar 2008 12:19:30 GMT (envelope-from phk@critter.freebsd.dk) To: Peter Jeremy From: "Poul-Henning Kamp" In-Reply-To: Your message of "Wed, 19 Mar 2008 17:44:33 +1100." <20080319064433.GA44676@server.vk2pj.dyndns.org> Date: Wed, 19 Mar 2008 12:19:29 +0000 Message-ID: <9664.1205929169@critter.freebsd.dk> Sender: phk@critter.freebsd.dk 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 12:19:33 -0000 In message <20080319064433.GA44676@server.vk2pj.dyndns.org>, Peter Jeremy write s: >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 was talking in the context of having a facility for spinning disks down vs. always letting them run. You're talking about when we spin them down, which is a matter of tuning. Yes, obviously our defaults should be sensible, as always. >>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. I'm not so sure, the chips have pretty good resolution and high accumulation rate, it's ACPI which only ask the chip every 30 seconds. >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. The problem with this approach, is that you need to accumulate current measurements at least 500 times per second, to get a realistic picture of the power content of the spikes. You can of course do a lot to smooth this out, but then it turns into (even more) of an electronics task. The only PSU's I know that can do this themselves are the HP/Agilent "extra 3" supplies like the 66311 and similar. If you want to measure on the high-voltage side, the best and cheapest strategy is to get a utility-class powermeter (like the DIN unit i linked to in the other mail) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.