Date: Fri, 7 Sep 2007 22:14:53 +0200 From: "Cyrille Szymanski" <cnszym@gmail.com> To: "William Grzybowski" <william88@gmail.com>, freebsd-acpi@freebsd.org Subject: Re: powerd algorithms Message-ID: <ba5115170709071314u3bd8242eif6a8e0b0351ccad1@mail.gmail.com> In-Reply-To: <632825b40709071127v63100e16i4fe4c006f96fd3ff@mail.gmail.com> References: <632825b40709062006n6d612c73r13c03aa16a6d5c2d@mail.gmail.com> <46E0F352.4090604@root.org> <ba5115170709071102u7c0d901le91eca9be1647ea2@mail.gmail.com> <632825b40709071127v63100e16i4fe4c006f96fd3ff@mail.gmail.com>
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> 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 ? Bye -- Cyrille
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