Power-Mgt (Was: Re: cvs commit: src/sys/i386/cpufreq est.c )

[Poul-Henning Kamp]

In message <20080318185435.GA2853 at lor.one-eyed-alien.net>, Brooks Davis writes:

>For amusement value, I had a dual P4-Xeon box hooked up to one once
>and found that power consumption with SETI at 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.

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.

Poul-Henning

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