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

On Tue, Mar 18, 2008 at 06:26:11PM +0000, Robert Watson wrote:

On Mon, 17 Mar 2008, Poul-Henning Kamp wrote:

In message <47DED21C.4070108@xxxxxxxxxxx>, Kris Kennaway writes:

I think this is a great idea, but one of the big problems is probably
going to be dealing with hardware quirks. e.g. we can't even enable
powerd by default because e.g. acpi_throttle hangs on some systems. It
might be tricky to get power management to the stage where it works for
everyone and can be done automatically.

I'd expect that this will improve over time, just like all other
technologies from ISA to PCI bus implementations did.

But yes, it will take time & effort, but given the current
cleantech/greentech buzz, I think we'd better get moving.

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. Those metrics may require knowledge
of statistics and a lifetime of experience to interpret correctly, but they
are still numbers that are easily generated and compared. To drive work in
power management, we would benefit from having similarly accessible
metrics. Are there any decent documents describing how to do power use
measurement, and are there any (relatively) accessible tools for doing it
with? For example, on notebooks, can we sample an ACPI value before/after
a benchmark, or do we really need to hook something up to the power supply
in order to get a useful number?

For servers, logging power meters with computer interfaces seem to be
fairly expensive, but accumulating or instantaneous ones you have to
look at to get data out of aren't too bad. For example, the Kill A Watt
meter available in the US is $20-30.

http://www.p3international.com/products/special/P4400/P4400-CE.html

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.

-- Brooks

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