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

In message <20080318182358.F34016@xxxxxxxxxxxxxxxxx>, 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@xxxxxxxxxxx | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
_______________________________________________
freebsd-arch@xxxxxxxxxxx mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-arch
To unsubscribe, send any mail to "freebsd-arch-unsubscribe@xxxxxxxxxxx"

Relevant Pages

  • Re: NEC Evaluations
    ... power measurement is a snap. ... do these measurements with traceability to the limits you suggest. ... is relative accuracy, not absolute accuracy, and the relative accuracy ... it performs power determination. ...
    (rec.radio.amateur.antenna)
  • Re: Gottlieb Bridge Rectifier Issues?
    ... voltage measurements are the only true measurement. ... this could only be a power on measurement. ... This is all in the guide. ...
    (rec.games.pinball)
  • Re: Landis aerobars
    ... He is clearly _not_ going for a small frontal area - he looks a lot like ... how aero a shape is) and frontal area are both fundamental to the drag ... even check for relative power losses in each position. ... The problem is that for coefficient of drag measurements (actually, ...
    (rec.bicycles.racing)
  • Re: Gottlieb Bridge Rectifier Issues?
    ... I agree with Ken when it comes to safety and comfort. ... voltage measurements are the only true measurement. ... this could only be a power on measurement. ...
    (rec.games.pinball)
  • Re: The power explanation
    ... at the output terminals is the conjugate of its load. ... Power Transfer Theoram. ... source resistance at the output terminals is 50 ohms. ... On those pages I report the results of measurements using the load- ...
    (rec.radio.amateur.antenna)