Date: Tue, 18 Mar 2008 19:52:02 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Robert Watson <rwatson@FreeBSD.org> Cc: arch@FreeBSD.org, Kris Kennaway <kris@FreeBSD.org> Subject: Re: Power-Mgt (Was: Re: cvs commit: src/sys/i386/cpufreq est.c ) Message-ID: <1278.1205869922@critter.freebsd.dk> In-Reply-To: Your message of "Tue, 18 Mar 2008 18:26:11 GMT." <20080318182358.F34016@fledge.watson.org>
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In message <20080318182358.F34016@fledge.watson.org>, Robert Watson writes: >I know we've talked about this, but I'll mention it for the benefits of the >mailing list: one of the things that makes performance an "easy" target is >that there are easy-to-gather metrics. [...] Are >there any decent documents describing how to do power use measurement, and are >there any (relatively) accessible tools for doing it with? I think performance and power-performance is pretty similar in this: you can easily collect some pretty crude performance indications and it takes a determined effort to get hard numbers. 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. When we talk about optimizing scheduling to keep chips powered off as much as possible, it will more than the average ampmeter to inform about the optimal algorithms. 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. Obviously, if you have access to a decent bench supply, you can run your laptop off that (take the battery out so charging does not 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. Summary: There isn't anything as handy as time(1), but it isn't rocket science either. -- 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.
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