Date: Mon, 10 Sep 2007 10:43:11 -0300 From: "William Grzybowski" <william88@gmail.com> To: "Kevin Oberman" <oberman@es.net> Cc: freebsd-acpi@freebsd.org Subject: Re: powerd algorithms Message-ID: <632825b40709100643t40c41376xc69e7096d637fa8c@mail.gmail.com> In-Reply-To: <20070907213724.F1D384500E@ptavv.es.net> References: <ba5115170709071314u3bd8242eif6a8e0b0351ccad1@mail.gmail.com> <20070907213724.F1D384500E@ptavv.es.net>
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On 9/7/07, Kevin Oberman <oberman@es.net> wrote: > > > 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 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
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