Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756690AbXINMh3 (ORCPT ); Fri, 14 Sep 2007 08:37:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751992AbXINMhV (ORCPT ); Fri, 14 Sep 2007 08:37:21 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.31.123]:59768 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751954AbXINMhU (ORCPT ); Fri, 14 Sep 2007 08:37:20 -0400 Date: Fri, 14 Sep 2007 14:38:16 +0200 From: Pavel Machek To: Thomas Gleixner Cc: "Rafael J. Wysocki" , Jeff Chua , rusty@rustycorp.com.au, vatsa@in.ibm.com, zwane@arm.linux.org.uk, kernel list , Len Brown Subject: Re: cpu hotplug support broken in 2.6.23-rc3 Message-ID: <20070914123816.GE1671@elf.ucw.cz> References: <20070827104350.GA2073@elf.ucw.cz> <20070903034720.GB3655@ucw.cz> <200709031219.12846.rjw@sisk.pl> <1188822917.3406.0.camel@chaos> <20070904072744.GA30474@atrey.karlin.mff.cuni.cz> <1189713695.3974.23.camel@chaos> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1189713695.3974.23.camel@chaos> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.16 (2007-06-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1884 Lines: 44 Hi! > > > What was the last known to work version ? > > > > I'm afraid I only turned on HIGH_RES_TIMERS in 2.6.23-rc1 > > timeframe... so I'm not sure if it ever worked for me. > > > > I can confirm it is working in 2.6.23-rc5 with highres disabled, and > > broken with highres enabled. NOHZ turns "waits for keypress during > > unplug/replug" into "just plain hangs". > > Ok, I can reproduce it and I tracked down what happens: > > When the CPU goes offline, the clock event source for this CPU (lapic) > is removed from the clock events framework. This also clears the > information that the CPU is using C-States which stop the local APIC > timer. > > Now you put the CPU online again and the local APIC timer is used, but > the C-State information is not evaluated again in ACPI. This means that > the clock events code does not know that the APIC might stop. In the > worst case this will happen and make the CPU wait for timer interrupts > forever. > > The problem only appears when you are on battery (c3/c4 available) or on > those broken machines, where C2 is in reality C3 (e.g. akpm's VAIO) > > I have an yet untested fix, which preserves the broadcast state across > the offline state, but Len is looking into it as well, whether we can > just reevaluate the power states (and the broadcast flags) when a cpu > becomes online again. If Len can do that easily for 2.6.23, I'd prefer > that. Is there a patch you want me to test? Or does Len have anything to play with? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - 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/