powerd algorithms

[William Grzybowski]

On 9/7/07, Kevin Oberman <oberman at es.net> wrote:
>
> > Date: Fri, 7 Sep 2007 22:14:53 +0200
> > From: "Cyrille Szymanski" <cnszym at gmail.com>
> > Sender: owner-freebsd-acpi at freebsd.org
> >
> > > Hi Cyrille,
> > >
> > > Would be nice if you can share you research about powerd with me, i am
> really interested in this subject...
> >
> > My biggest concerns (and why I more or less lost interest in this
> > project) are that :
> > 1. I believe FLAT to be very close to, if not the best universal
> > algorithm possible;
> > 2. I was unable to find a decent way to quantify the power savings of
> > each approach other than by simulation or using current probes.
> >
> > Power consumption depends both on frequency and workload and since I
> > have no idea how CPUs behave in practice I cannot design any smarter
> > solution. The best solution is likely to be something specific to each
> > CPU model/brand (see bullet 1). This would require building a database
> > of the optimum settings for each CPU model. I am not sure we find
> > enough people willing to experiment, unless... (see bullet 2).
> >
> > Note: I am not convinced that my laptop uses less power when running
> > at its lowest frequency when I see the heat that it emits in that
> > mode.
> >
> > > Actually the powerd has 3 modes right? [min,max,adaptive]
> > > The adaptive uses the relation about idle and total usage, but just
> one by one, i was thinking in use a short historical of this cpu usage
> related by idle and create some profiles over it (like ondemand and
> conservative in linux)...
> >
> > AFAIK the 'adaptive' mode increases by two steps and decreases by one
> > step (this would be more responsive). If you look at CVS revisions for
> > powerd.c you'll see what has been tried over the years (rev 1.9 for
> > example)
> http://www.freebsd.org/cgi/cvsweb.cgi/src/usr.sbin/powerd/powerd.c
> >
> > Have you checked the research papers describing approaches such as
> > PAST, FLAT etc. ? I did not investigate the linux 'ondemand' and



I have to take a look in ondemand code, but i always worked fine to me,
maybe it really worth a try as you said.

> 'conservative' modes but maybe they are worth a try. As I understand
> > it, FreeBSD lacks only the 'ondemand' mode ?


Not completely, but I will take a look.


Cyrille,
>
> Three ago I did some analysis of the effects of power management on some
> laptops of that era. Most had either no voltage-frequency management or
> only the basic SST...not EST. I really should do some current testing. I
> still think I have all of the scripts I used to do this, but all testing
> was done at 100% CPU utilization or idle.
>
> I found that simple CPU throttling was not too effective as a power
> management tool. Not totally ineffective, but not very good. SpeedStep
> was effective. I suspect EST with both voltage and frequency control
> would be much better as would the AMD and maybe VIA equivalents.
>
> I was planning on modifying my tests to report at various levels of CPU
> utilization, but then got tied up on other things and have not gotten
> back to it. I did determine that running at 800 MHz frequency (SST) with
> the CPU loaded at 90% used quite a bit more power than running at 1.2
> GHZ at 60%. I would be happy to provide my perl scripts to someone who
> would like to expand them to test at other than 100% and 0% load.
>

Hi Kevin,

You can send this scripts to me, thanks.
As I can understand you are saying throttling is not that effective about
power consuming, but I guess this is not the unique point to discuss. Tell
me if i got i wrong ;)

Better than this is just use low frequencies when you don't need higher
process power and with it, take down the >cpu temperature< and less use of
the cooler...

Bye.


-- 
William Grzybowski
------------------------------------------
Jabber: william88 at gmail dot com
Curitiba/PR - Brazil