Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933227AbaBAPbx (ORCPT ); Sat, 1 Feb 2014 10:31:53 -0500 Received: from mail-qa0-f49.google.com ([209.85.216.49]:44516 "EHLO mail-qa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751944AbaBAPbv (ORCPT ); Sat, 1 Feb 2014 10:31:51 -0500 Date: Sat, 1 Feb 2014 10:31:47 -0500 (EST) From: Nicolas Pitre To: "Brown, Len" cc: Arjan van de Ven , Daniel Lezcano , Preeti U Murthy , Peter Zijlstra , Preeti Murthy , "mingo@redhat.com" , Thomas Gleixner , "Rafael J. Wysocki" , LKML , "linux-pm@vger.kernel.org" , Lists linaro-kernel Subject: RE: [RFC PATCH 3/3] idle: store the idle state index in the struct rq In-Reply-To: <1A7043D5F58CCB44A599DFD55ED4C948452D34DC@FMSMSX106.amr.corp.intel.com> Message-ID: References: <1391090962-15032-1-git-send-email-daniel.lezcano@linaro.org> <1391090962-15032-4-git-send-email-daniel.lezcano@linaro.org> <20140130153150.GD5002@laptop.programming.kicks-ass.net> <52EA7D8A.6080604@linaro.org> <20140130163501.GG5002@laptop.programming.kicks-ass.net> <52EA8B07.6020206@linaro.org> <20140131090230.GM5002@laptop.programming.kicks-ass.net> <52EB6F65.8050008@linux.vnet.ibm.com> <52EBBC23.8020603@linux.intel.com> <52EBC33A.6080101@linaro.org> <52EBC645.2040607@linux.intel.com> <1A7043D5F58CCB44A599DFD55ED4C948452D34DC@FMSMSX106.amr.corp.intel.com> User-Agent: Alpine 2.11 (LFD 23 2013-08-11) 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 On Sat, 1 Feb 2014, Brown, Len wrote: > > Right now (on ARM at least but I imagine this is pretty universal), the > > biggest impact on information accuracy for a CPU depends on what the > > other CPUs are doing. The most obvious example is cluster power down. > > For a cluster to be powered down, all the CPUs sharing this cluster must > > also be powered down. And all those CPUs must have agreed to a possible > > cluster power down in advance as well. But it is not because an idle > > CPU has agreed to the extra latency imposed by a cluster power down that > > the cluster has actually powered down since another CPU in that cluster > > might still be running, in which case the recorded latency information > > for that idle CPU would be higher than it would be in practice at that > > moment. > > That will not work. What will not work? > When a CPU goes idle, it uses the CURRENT criteria for entering that state. > If the criteria change after it has entered the state, are you going > to wake it up so it can re-evaluate? No. That's not what I'm saying at all. > That is why the state must describe the worst case latency > that CPU may see when waking from the state on THAT entry. No disagreement there. Isn't that what I'm saying? > That is why we use the package C-state numbers to describe > core C-states on IA. And your point is? Nicolas -- 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/