Date: Fri, 07 Sep 2007 14:37:24 -0700 From: "Kevin Oberman" <oberman@es.net> To: "Cyrille Szymanski" <cnszym@gmail.com> Cc: freebsd-acpi@freebsd.org Subject: Re: powerd algorithms Message-ID: <20070907213724.F1D384500E@ptavv.es.net> In-Reply-To: Your message of "Fri, 07 Sep 2007 22:14:53 %2B0200." <ba5115170709071314u3bd8242eif6a8e0b0351ccad1@mail.gmail.com>
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--==_Exmh_1189201044_36704P Content-Type: text/plain; charset=us-ascii Content-Disposition: inline > Date: Fri, 7 Sep 2007 22:14:53 +0200 > From: "Cyrille Szymanski" <cnszym@gmail.com> > Sender: owner-freebsd-acpi@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 > 'conservative' modes but maybe they are worth a try. As I understand > it, FreeBSD lacks only the 'ondemand' mode ? 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. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: oberman@es.net Phone: +1 510 486-8634 Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751 --==_Exmh_1189201044_36704P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (FreeBSD) Comment: Exmh version 2.5 06/03/2002 iD8DBQFG4cSUkn3rs5h7N1ERAlcaAKCCyAldmCMMRqBNY3e4JyYsKxC9mgCgpZSX QxNk42y3CO1tmr7aPU75zQk= =Eoe2 -----END PGP SIGNATURE----- --==_Exmh_1189201044_36704P--
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