Date: Tue, 18 Mar 2008 14:43:38 -0700 From: Bakul Shah <bakul@bitblocks.com> To: "Poul-Henning Kamp" <phk@phk.freebsd.dk> Cc: arch@freebsd.org, Brooks Davis <brooks@freebsd.org>, Robert Watson <rwatson@freebsd.org> Subject: Re: Power-Mgt (Was: Re: cvs commit: src/sys/i386/cpufreq est.c ) Message-ID: <20080318214338.EB09F5B3B@mail.bitblocks.com> In-Reply-To: Your message of "Tue, 18 Mar 2008 19:59:40 -0000." <1362.1205870380@critter.freebsd.dk>
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On Tue, 18 Mar 2008 19:59:40 -0000 "Poul-Henning Kamp" <phk@phk.freebsd.dk> wrote: > In message <20080318185435.GA2853@lor.one-eyed-alien.net>, Brooks Davis write > s: > > >For amusement value, I had a dual P4-Xeon box hooked up to one once > >and found that power consumption with SETI@Home running was about 10W > >_lower_ than idle. > > That is a very good indication that the meter is a piece of crap that > does not have sufficient measurement rate to do a relevant job. You are likely right but it is also possible the system is poorly designed or broken in some way and does in fact draw more power when idle. Brooks ought to hook up his particular p4-xeon box to another brand meter to verify. > Unfortunately, that is the case for most of the gadgets you can buy > in shops. > > In general, you are much better off buying the real thing, for instance > a single-phase DIN power-meter like: > > http://www.metermaid.co.uk/din_rail_tech_info.html > > They cost less than EUR100/USD150 and have 1% accuracy. > > The "SO" output can be hooked up to a parallel or serial port and > you can accumulate and read the number of pulses using the PPS-API, > giving you, in this case, 500mWh resolution. I have been pretty happy with the Wattsup Pro meter but I admit I have not calibrated with to any known good reference for computer loads. It does a pretty accurate job on constant loads (verified with a DMM with good AC amps capability). It measures power down to a watt or so, with 100mWh resolution. Very useful for measuring standby mode power use (chargers, computer, laser printer, TV, phone, etc. -- can easily add up to over a Megawatt-hour a year!). I have the older serial only meter but now it comes with a USB port (about $130) https://www.doubleed.com/secure/products.php
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