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

[Bakul Shah]

On Tue, 18 Mar 2008 19:59:40 -0000 "Poul-Henning Kamp" <phk at phk.freebsd.dk>  wrote:
> In message <20080318185435.GA2853 at 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 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.

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