From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760343Ab2BJWfS (ORCPT ); Fri, 10 Feb 2012 17:35:18 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:46957 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753226Ab2BJWfQ (ORCPT ); Fri, 10 Feb 2012 17:35:16 -0500 From: "Rafael J. Wysocki" To: Alan Stern Subject: Re: [PATCH 0/4] CPU hotplug, cpusets: Fix CPU online handling related to cpusets Date: Fri, 10 Feb 2012 23:39:02 +0100 User-Agent: KMail/1.13.6 (Linux/3.3.0-rc2+; KDE/4.6.0; x86_64; ; ) Cc: Peter Zijlstra , paulmck@linux.vnet.ibm.com, Ingo Molnar , "Srivatsa S. Bhat" , paul@paulmenage.org, tj@kernel.org, frank.rowand@am.sony.com, pjt@google.com, tglx@linutronix.de, lizf@cn.fujitsu.com, prashanth@linux.vnet.ibm.com, vatsa@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "akpm@linux-foundation.org" References: In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201202102339.02702.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday, February 10, 2012, Alan Stern wrote: > On Fri, 10 Feb 2012, Peter Zijlstra wrote: > > > Now the whole problem here seems to be that suspend uses cpu-hotplug to > > reduce the machine to UP -- I've no clue why it does that but I can > > imagine its because the BIOS calls only work on CPU0 and/or the resume > > only wakes CPU0 so you have to bootstrap the SMP thing again.. Yes, that's the main problem. > > Some suspend person wanna clarify? Rafael? > > If I understand correctly, ACPI requires that only CPU0 be running when > the system is suspended (i.e., your guess is right). Of course, this > doesn't apply to non-ACPI systems, but it's easiest to do the same > thing everywhere. That's correct. Plus we have some code in the kernel (syscore_ops in general) that assumes to be executed on one CPU with interrupts off. Plus I'm not sure how the ACPI low-level suspend is going to behave if it's not executed on the boot CPU. > > Anyway, the whole suspend case is magic anyway since all tasks will have > > been frozen, so we could simply leave all of cpuset alone and ignore the > > hotplug notifier on CPU_TASKS_FROZEN callbacks, hmm? > > I don't see why not. Presumably no CPUs will be added or removed while > the system is asleep. ACPI explicitly forbids that level of hardware reconfiguration in a sleep state (even in S4), AFAICS. Still, people may try to do that ... Thanks, Rafael