From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Machek Subject: Re: nokia 770 [was Re: community PM requirements/issues and PowerOP] Date: Thu, 14 Dec 2006 14:56:10 +0000 Message-ID: <20061214145609.GA4451@ucw.cz> References: <457FEE17.8080806@gmail.com> <20061213210359.GC11843@elf.ucw.cz> <200612131332.58606.david-b@pacbell.net> <20061213215351.GE2418@redhat.com> <5062AF8D-E97F-41D2-8602-59578F2B4655@comcast.net> <20061213225802.GN2418@redhat.com> <458123F5.6090104@gmail.com> <20061214121214.GR2418@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.osdl.org Errors-To: linux-pm-bounces@lists.osdl.org To: Vitaly Wool Cc: linux-pm@lists.osdl.org, Amit Kucheria , Matthew Locke , scott.preece@motorola.com List-Id: linux-pm@vger.kernel.org > >But what sense does it make for a user,sysadmin or = > >application > >to change voltage? If any of these want to save power, = > >they do so > >by a) doing less work, and then b) lowering the clock = > >speed as this > >is inherently tied to voltage. > = > It makes sense to perform changing an operating point = > dynamically in > userland. In very special cases, yes. > That said, voltage should be accessible from userland. Why? If few states differ in voltage but not frequency, the only user-visible thing is different latency of enter/exit. If you only have two voltages per frequency (as it was shown in examples here)... just add 1Hz to make difference between the two. ...but I guess you should teach cpufreq's ondemand governor to deal with different latencies for different voltages. Before that is done and shown to have significant power-saving impact, userspace interface debate is useless. Pavel -- = Thanks for all the (sleeping) penguins.