Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933179Ab0FQTAj (ORCPT ); Thu, 17 Jun 2010 15:00:39 -0400 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 Date: Thu, 17 Jun 2010 15:00:15 -0400 (EDT) From: Len Brown X-X-Sender: lenb@localhost.localdomain To: Igor.Stoppa@nokia.com Cc: linux-pm@lists.osdl.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org Subject: RE: [linux-pm] RFC: /sys/power/policy_preference In-reply-to: Message-id: References: User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-version: 1.0 Content-type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1904 Lines: 49 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/