Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755495AbXLJLXg (ORCPT ); Mon, 10 Dec 2007 06:23:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751943AbXLJLX3 (ORCPT ); Mon, 10 Dec 2007 06:23:29 -0500 Received: from E23SMTP03.au.ibm.com ([202.81.18.172]:34089 "EHLO e23smtp03.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751936AbXLJLX2 (ORCPT ); Mon, 10 Dec 2007 06:23:28 -0500 Date: Mon, 10 Dec 2007 16:38:18 +0530 From: Gautham R Shenoy To: Ingo Molnar Cc: Jiri Slaby , Andrew Morton , linux-kernel@vger.kernel.org, "Rafael J. Wysocki" , Arjan van de Ven , Thomas Gleixner , Linux-pm mailing list , Dipankar Sarma Subject: Re: broken suspend (sched related) [Was: 2.6.24-rc4-mm1] Message-ID: <20071210110818.GC12880@in.ibm.com> Reply-To: ego@in.ibm.com References: <20071208083939.GD30997@elte.hu> <475A629C.7010408@gmail.com> <20071208152447.GA30270@elte.hu> <475B24F4.3090904@gmail.com> <20071209074647.GE22981@elte.hu> <20071210081952.GA7215@in.ibm.com> <475CFF01.2090502@gmail.com> <20071210091052.GA14487@elte.hu> <20071210101500.GB12880@in.ibm.com> <20071210102157.GB31103@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20071210102157.GB31103@elte.hu> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3812 Lines: 111 On Mon, Dec 10, 2007 at 11:21:57AM +0100, Ingo Molnar wrote: > > * Gautham R Shenoy wrote: > > > > i'm wondering, what's the proper CPU-hotplug safe sequence here > > > then? I'm picking a CPU number from cpu_online_map, and that CPU > > > could go away while i'm still using it, right? What's saving us > > > here? > > > > In this particular case, we are trying to see if any task on a > > particular cpu has not been scheduled for a really long time. If we do > > this check on a cpu which has gone offline, then a) If the tasks have > > not been migrated on to another cpu yet, we will still perform that > > check and yell if something has been holding any task for a > > sufficiently long time. b) If the tasks have been migrated off, then > > we have nothing to check. > > say we've got 100 CPUs, so we've got 100 watchdog tasks running - one > for each CPU. Checking for hung tasks is a global operation not a > per-CPU operation (we iterate over the global tasklist), hence only one > CPU should really be calling this function. That online-cpus logic > achieves this by picking a single CPU. Perhaps it would be better to > keep a hung_task_checker_cpu variable that is driven from a > CPU-hotplug-down notifier? That way if a CPU is brought down we can > update hung_task_checker_cpu to another, still-online CPU. (this would > also be faster, because event-driven) Do you mean something like this? From: Gautham R Shenoy softlockup: update check_cpu during cpu-hotplug Update the check_cpu value during a cpu-hotplug operation so that we don't check for hung tasks on a cpu which is about to go offline. Signed-off-by: Gautham R Shenoy Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Jiri Slaby --- kernel/softlockup.c | 14 ++++++++++++-- 1 files changed, 12 insertions(+), 2 deletions(-) diff --git a/kernel/softlockup.c b/kernel/softlockup.c index 576eb9c..b1a8c7c 100644 --- a/kernel/softlockup.c +++ b/kernel/softlockup.c @@ -194,6 +194,9 @@ static void check_hung_uninterruptible_tasks(int this_cpu) read_unlock(&tasklist_lock); } + +static int check_cpu = -1; + /* * The watchdog thread - runs every second and touches the timestamp. */ @@ -219,8 +222,6 @@ static int watchdog(void *__bind_cpu) /* * Only do the hung-tasks check on one CPU: */ - check_cpu = any_online_cpu(cpu_online_map); - if (this_cpu != check_cpu) continue; @@ -255,6 +256,7 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) break; case CPU_ONLINE: case CPU_ONLINE_FROZEN: + check_cpu = any_online_cpu(cpu_online_map); wake_up_process(per_cpu(watchdog_task, hotcpu)); break; #ifdef CONFIG_HOTPLUG_CPU @@ -265,6 +267,14 @@ cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu) /* Unbind so it can run. Fall thru. */ kthread_bind(per_cpu(watchdog_task, hotcpu), any_online_cpu(cpu_online_map)); + case CPU_DOWN_PREPARE: + case CPU_DOWN_PREPARE_FROZEN: + if (hotcpu == check_cpu) { + cpumask_t temp_cpu_online_map = cpu_online_map; + cpu_clear(hotcpu, temp_cpu_online_map); + check_cpu = any_online_cpu(temp_cpu_online_map); + } + break; case CPU_DEAD: case CPU_DEAD_FROZEN: p = per_cpu(watchdog_task, hotcpu); > > Ingo Thanks and Regards gautham. -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" -- 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/