RFC: powerd algorithms enhancements

[Alexander Motin]

The discussion of this is going on mobile@:

-------- Original Message --------
Subject: RFC: powerd algorithms enhancements
Date: Wed, 05 Nov 2008 22:57:55 +0200
From: Alexander Motin <mav at FreeBSD.org>
To: freebsd-mobile at FreeBSD.org

Hi.

I would like to propose the patch for powerd that fixes some issues,
makes it more universal and on my opinion more usable. The main ideas of
mine were:

1. To make it more SMP polite. Previous version uses average CPU load
that leads to the often load underestimation. It make powerd with
default configuration unusable on systems with more then 2 CPUs. I
propose to use summary load instead of average one. IMO this is the best
we can do without specially tuned scheduler. Also as soon as measuring
total load on SMP systems is more useful then total idle, I have
switched to it.

2. To make powerd's operation independent from number and size of
frequency levels I have added internal frequency counter which
translated into real frequencies only on a last stage and only as good
as gone. Some systems may have only several power levels, while mine has
17 of them, so adaptation time in completely different. It would be good
if algorithm was not depending on it.

3. As part of previous I have changed adaptive mode to rise frequency on
demand up to 2 times and fall on 1/8 per time internal.

4. For desktop (AC-powered) systems I have added one more mode -
"hiadaptive". It rises frequency twice faster, drops it 4 times slower,
prefers twice lower CPU load and has additional delay before leaving the
highest frequency after the period of maximum load. This mode was
specially made to improve interactivity of the systems where operation
capabilities are more significant then power consumption, but keeping
maximum frequency all the time is not needed.

5. I have reduced polling interval from 1/2 to 1/4 of second. It is not
important for algorithm math now, but gives better system interactivity.

-- 
Alexander Motin