From mboxrd@z Thu Jan 1 00:00:00 1970 From: Len Brown Subject: RE: [linux-pm] RFC: /sys/power/policy_preference Date: Thu, 17 Jun 2010 15:00:15 -0400 (EDT) Message-ID: References: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: Received: from vms173013pub.verizon.net ([206.46.173.13]:28483 "EHLO vms173013pub.verizon.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757354Ab0FQTAh (ORCPT ); Thu, 17 Jun 2010 15:00:37 -0400 In-reply-to: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Igor.Stoppa@nokia.com Cc: linux-pm@lists.osdl.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org On Thu, 17 Jun 2010, Igor.Stoppa@nokia.com wrote: > i do understand that you are mostly targetting acpi based systems, > but even there, based on static leaks, it might not be always true > that lower frequencies are correlated to higher power savings > (or maybe i have misunderstood your draft - i am not so fluent in acpi) Right, my assertion is that ondemand deals only with P-states, where, by defintion, the deeper the P-state the lower the voltage, the higher the efficiency. I assume that ondemand is not used to enable T-states where the clock is throttled w/o lowering the voltage. I put a note to try to make that clear under max_powersave: "ondemand: min P-state (do not invoke T-states)" Of course it is also possible for a processor to do a poor job implementing P-states and a great job optimizing idle states such that race to idle were always a win. However, on such a processor it would make more sense to simply disable P-states. > > it is likely > > that some users would want to use "powersave" when on > > battery and perhaps shift to "performance" on A/C. > > if we consider also the thermal envelope and the fact that "performance" > might steal power from a charging battery, even ton A/C it might not be > possible to settle down in one state permanently. > > Or do you expect other mechanisms to intervene? Typical laptop BIOS commonly implement a scheme where they maximize performance on AC and bias towards saving energy on DC. That, of course, is just one example use-model. Here Linux user-space can choose whatever policy makes sense for them at run-time. cheers, -Len Brown, Intel Open Source Technology Center