Well, if you're using a CPU that supports the same CPU frequency at multiple voltages, then it's useful to be able to determine the voltage as well as the frequency. You can't assume you want to use the lowest voltage, because voltage changes may take significantly longer than frequency changes. In some situations you may want to contrain your frequency shifting to stay at the current voltage, in other cases not, depending on what you know about the current task load. scott | From linux-pm-bounces at lists.osdl.org Thu Dec 14 07:36:57 2006 | Date: Thu, 14 Dec 2006 08:17:12 -0500 | From: Dave Jones<davej at redhat.com> | User-Agent: Mutt/1.4.2.2i | X-Spam-Status: No, hits=-1.885 required=5 tests=AWL,OSDL_HEADER_LISTID_KNOWN,OSDL_HEADER_SUBJECT_BRACKETED | Cc: Pavel Machek<pavel at ucw.cz>, Amit Kucheria<amit.kucheria at nokia.com>, | Precedence: list | | On Thu, Dec 14, 2006 at 04:01:58PM +0300, Vitaly Wool wrote: | > On 12/14/06, Dave Jones <davej at redhat.com> wrote: | > > | > > | > > 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. | | An operating point does not have to revolve around the voltage, nor should it. | Fill out the following. | | * A sysadmin wants to set the CPU voltage to 1.5V because _________________ | | * A user wants to set the CPU voltage to 1.5V because _________________ | | * An application wants to dynamically set the voltage rather than the | frequency because ______________________ | | | > That said, voltage should be accessible from userland. | | Try again. It's completely the wrong knob to be turning. | | Dave | | -- | http://www.codemonkey.org.uk | _______________________________________________ | linux-pm mailing list | linux-pm at lists.osdl.org | https://lists.osdl.org/mailman/listinfo/linux-pm | -- scott preece motorola mobile devices, il67, 1800 s. oak st., champaign, il 61820 e-mail: preece at motorola.com fax: +1-217-384-8550 phone: +1-217-384-8589 cell: +1-217-433-6114 pager: 2174336114 at vtext.com
