HEADSUP: cpufreq import complete, acpi_throttling changed

[Kevin Oberman]

> Date: Mon, 14 Feb 2005 22:19:48 +0100
> From: Pawel Worach <pawel.worach at telia.com>
> Sender: owner-freebsd-acpi at freebsd.org
> 
> Nate Lawson wrote:
> > Any word if the patch I sent helped?
> 
> Hi, sorry for the delay. I bumped the number of retries to 2000 and I
> can still repro. the error if the cpu has some load, I believe that is
> expected. Even when "idle" (gnome desktop running) it works fine with
> 100, I think the first time I tested it I had mplayer running. I can't
> see a real-life reason for bumping the number of retries, from all
> speeds above 200Mhz I can step back up to 1.7Ghz without problems
> under light cpu load. The power_profile script should probably have a
> min limit, 75Mhz is ridiculous :)
> 
> Another cool thing would be if the speed could be stepped
> automagically based on current battery level, that would likely be the
> job for a powerd(8).

I've been things about this, too, and I think that stepping things down
with battery level is not the answer. I think it MIGHT make sense to do
so based on battery discharge rate. This would allow a user to configure
an approximate battery "lifetime". It is especially important as
batteries wear and, if two batteries are present, one discharges faster
than the other.

The other issue is thermal. I would assume that the frequency should be
decreased when _PSV is reached, but should it continue to drop the
frequency until the temperature stabilizes or until it drops to _PSV.  I
believe the latter is a better choice, especially as the effect is not
quite instantaneous, and since it is only read by ACPI at fairly long
intervals. This means that the adjustment should not be too aggressive
to prevent continual oscillation of the frequency and temperature.

And when do you start increasing the frequency again when temperature
drops? Once again, you want to reach a thermal stability and not
oscillate around _PSV (or at least do so slowly. As there is probably
substantial variation between systems, so a settable hysteresis is
probably needed for really good results. (This gets worse for system
which don't support both throttling and frequencies.)

And, should TCC be folded into the equation for P4 systems? After all,
that's what it's for. I dont; see any way to set TCC to automatic at the
moment, but that could be a significant tool in thermal stability.
(There may be a way, but I didn't see it in the sources.)

Lot of things to consider.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634