Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756444AbXJAV7T (ORCPT ); Mon, 1 Oct 2007 17:59:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753335AbXJAV7K (ORCPT ); Mon, 1 Oct 2007 17:59:10 -0400 Received: from www.tglx.de ([62.245.132.106]:36501 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751596AbXJAV7J (ORCPT ); Mon, 1 Oct 2007 17:59:09 -0400 Date: Mon, 1 Oct 2007 23:58:07 +0200 (CEST) From: Thomas Gleixner To: Andi Kleen cc: Arjan van de Ven , David Bahi , LKML , linux-rt-users@vger.kernel.org, Andrew Morton , Ingo Molnar , Gregory Haskins Subject: Re: nmi_watchdog fix for x86_64 to be more like i386 In-Reply-To: <200710012341.53169.ak@suse.de> Message-ID: References: <46FA4A800200006C000192FE@sinclair.provo.novell.com> <20071001125626.32eb6d0b@laptopd505.fenrus.org> <200710012341.53169.ak@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1585 Lines: 40 On Mon, 1 Oct 2007, Andi Kleen wrote: > > > IRQ_NOBALANCING is not preventing cpu unplug. It moves the affinity to the > > next CPU, but the check in NMI watchdog for CPU == 0 would not longer > > work. > > That cannot happen right now because cpu_disable() on both i386/x86-64 > reject CPU #0. So just setting IRQ_NOBALANCING is sufficient and both > do that already. I was wrong earlier in being concerned about this. > > > int tick_do_broadcast(cpumask_t mask) > > @@ -137,6 +147,7 @@ int tick_do_broadcast(cpumask_t mask) > > cpu_clear(cpu, mask); > > td = &per_cpu(tick_cpu_device, cpu); > > td->evtdev->event_handler(td->evtdev); > > + tick_broadcast_account(cpu); > > That would not handle the case with a single CPU running only > irq 0 but not broadcasting I think. Hmm. The only situation where this can happen is when you add "nolapic_timer" to the command line on a single CPU system. We do not register the lapic "dummy" clock event device then. > I believe > ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt/patches/fix-watchdog > is the correct fix Yup, I completely missed the fact, that we reject CPU#0 unplugging, so your fix seems indeed to be more correct and simpler. OTOH, the accounting hook would allow us to remove the IRQ#0 -> CPU#0 restriction. Not sure whether it's worth the trouble. tglx - 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/