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From: Gautham R Shenoy <ego@in.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Jiri Slaby <jirislaby@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linux-pm mailing list <linux-pm@lists.linux-foundation.org>,
	Dipankar Sarma <dipankar@in.ibm.com>
Subject: Re: broken suspend (sched related) [Was: 2.6.24-rc4-mm1]
Date: Mon, 10 Dec 2007 16:38:18 +0530	[thread overview]
Message-ID: <20071210110818.GC12880@in.ibm.com> (raw)
In-Reply-To: <20071210102157.GB31103@elte.hu>

On Mon, Dec 10, 2007 at 11:21:57AM +0100, Ingo Molnar wrote:
> 
> * Gautham R Shenoy <ego@in.ibm.com> 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 <ego@in.ibm.com>

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 <ego@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linuxtronix.de>
Cc: Jiri Slaby <jirislaby@gmail.com>
---

 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!"

  reply	other threads:[~2007-12-10 11:23 UTC|newest]

Thread overview: 112+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-12-05  5:17 2.6.24-rc4-mm1 Andrew Morton
2007-12-05  9:15 ` 2.6.24-rc4-mm1: kobj changes fallout on powerpc Olof Johansson
2007-12-05 13:11   ` Kamalesh Babulal
2007-12-05 15:46     ` Greg KH
2007-12-05 14:12 ` 2.6.24-rc4-mm1 kobject changes broken with hvcs driver " Kamalesh Babulal
2007-12-05 15:47   ` Greg KH
2007-12-06 18:19   ` Balbir Singh
2007-12-06 18:50     ` Greg KH
2007-12-06 18:49       ` Kamalesh Babulal
2007-12-06 18:58       ` Balbir Singh
2007-12-06 19:21         ` Badari Pulavarty
2007-12-07  1:29           ` Balbir Singh
2007-12-06 20:31         ` Greg KH
2007-12-06 23:54           ` Badari Pulavarty
2007-12-07  0:32             ` Greg KH
2007-12-07  3:02               ` Kamalesh Babulal
2007-12-07  5:14                 ` Greg KH
2007-12-07 22:01                   ` Balbir Singh
2007-12-05 23:41 ` 2.6.24-rc4-mm1: hostbyte=0x01 driverbyte=0x00 (now bisected) Alexey Dobriyan
2007-12-06  7:52   ` Hannes Reinecke
2007-12-06 12:08     ` Jens Axboe
2007-12-06 19:19     ` Alexey Dobriyan
2007-12-06  3:15 ` 2.6.24-rc4-mm1 Kernel build fails on S390x Kamalesh Babulal
2007-12-06  7:19   ` Andrew Morton
2007-12-06  6:59 ` 2.6.24-rc4-mm1 Reuben Farrelly
2007-12-06  7:09   ` 2.6.24-rc4-mm1 David Miller
2007-12-07 13:16     ` 2.6.24-rc4-mm1 Ilpo Järvinen
2007-12-12 17:57       ` 2.6.24-rc4-mm1 Cedric Le Goater
2007-12-06  7:35   ` 2.6.24-rc4-mm1 Andrew Morton
2007-12-10 12:24     ` 2.6.24-rc4-mm1 Ilpo Järvinen
2007-12-10 20:05       ` 2.6.24-rc4-mm1 Ilpo Järvinen
2007-12-12 19:21       ` 2.6.24-rc4-mm1 Cedric Le Goater
2007-12-13 17:38         ` tcp_sacktag_one() WARNING (was Re: 2.6.24-rc4-mm1) Cedric Le Goater
2007-12-06 11:49 ` 2.6.24-rc4-mm1 Valdis.Kletnieks
2007-12-06 12:04   ` 2.6.24-rc4-mm1 Andrew Morton
2007-12-06 19:18     ` 2.6.24-rc4-mm1 Valdis.Kletnieks
2007-12-06 19:38       ` 2.6.24-rc4-mm1 Greg KH
2007-12-06 20:04         ` 2.6.24-rc4-mm1 Valdis.Kletnieks
2007-12-06 22:04         ` [dm-devel] 2.6.24-rc4-mm1 Kay Sievers
2007-12-06 22:12           ` Alasdair G Kergon
2007-12-06 23:12           ` Valdis.Kletnieks
2007-12-06 23:24             ` Kay Sievers
2007-12-07 18:20               ` Valdis.Kletnieks
2007-12-07 18:44                 ` Kay Sievers
2007-12-07 20:28                   ` Valdis.Kletnieks
2007-12-07 20:49                     ` Kay Sievers
2007-12-06 22:28 ` 2.6.24-rc4-mm1: VDSOSYM build error Laurent Riffard
2007-12-06 22:37   ` Andrew Morton
2007-12-06 23:28     ` Miles Lane
2007-12-06 23:34       ` Andrew Morton
2007-12-06 23:47         ` Miles Lane
2007-12-07 10:36         ` Ingo Molnar
2007-12-07  1:14     ` [PATCH x86/mm] x86 vDSO: canonicalize sysenter .eh_frame Roland McGrath
2007-12-07  1:27       ` Harvey Harrison
2007-12-07  3:27         ` Miles Lane
2007-12-07  9:44       ` Ingo Molnar
2007-12-07  2:12 ` 2.6.24-rc4-mm1 Dave Young
2007-12-07 22:22   ` 2.6.24-rc4-mm1 Luis R. Rodriguez
2007-12-10  1:07     ` 2.6.24-rc4-mm1 Dave Young
2007-12-09 17:55   ` 2.6.24-rc4-mm1 Nick Kossifidis
     [not found] ` <E1J0Yfy-0001V7-Rr@localhost>
2007-12-07  8:35   ` [PATCH BUGFIX] hid: the `bit' in hidinput_mapping_quirks() is an out parameter Fengguang Wu
2007-12-10 10:03     ` Jiri Kosina
2007-12-07 14:34 ` broken suspend (sched related) [Was: 2.6.24-rc4-mm1] Jiri Slaby
2007-12-07 15:11   ` Ingo Molnar
2007-12-07 17:51     ` Ingo Molnar
2007-12-08  8:10       ` Jiri Slaby
2007-12-08  8:39         ` Ingo Molnar
2007-12-08  9:23           ` Jiri Slaby
2007-12-08 15:24             ` Ingo Molnar
2007-12-08 17:34               ` Jiri Slaby
2007-12-08 17:43               ` Jiri Slaby
2007-12-09  8:06                 ` Ingo Molnar
2007-12-08 23:12               ` Jiri Slaby
2007-12-09  7:46                 ` Ingo Molnar
2007-12-09  9:09                   ` Jiri Slaby
2007-12-10  8:19                   ` Gautham R Shenoy
2007-12-10  8:55                     ` Jiri Slaby
2007-12-10  9:10                       ` Ingo Molnar
2007-12-10 10:15                         ` Gautham R Shenoy
2007-12-10 10:21                           ` Ingo Molnar
2007-12-10 11:08                             ` Gautham R Shenoy [this message]
2007-12-10 11:28                               ` Ingo Molnar
2007-12-10 11:49                                 ` Gautham R Shenoy
2007-12-10  9:29                     ` Ingo Molnar
2007-12-07 18:20 ` [PATCH] md: balance braces in raid5 debug code Mariusz Kozlowski
2007-12-08  0:04 ` 2.6.24-rc4-mm1: undefined reference to `compat_sys_timerfd' on sparc64 Mariusz Kozlowski
2007-12-08  0:08   ` Andrew Morton
2007-12-08  9:17     ` Mariusz Kozlowski
2007-12-11 10:15     ` David Miller
2007-12-08 18:20 ` 2.6.24-rc4-mm1: some issues " Mariusz Kozlowski
2007-12-08 18:22   ` Andrew Morton
2007-12-09  8:45     ` David Miller
2007-12-09  9:03       ` Andrew Morton
2007-12-10 14:48 ` 2.6.24-rc4-mm1 Reuben Farrelly
2007-12-10 21:11   ` 2.6.24-rc4-mm1 Andrew Morton
2007-12-11 14:12     ` 2.6.24-rc4-mm1 Reuben Farrelly
2007-12-11 16:20 ` 2.6.24-rc4-mm1 Martin Bligh
2007-12-11 16:59   ` 2.6.24-rc4-mm1 Randy Dunlap
2007-12-11 17:50     ` 2.6.24-rc4-mm1 Martin Bligh
     [not found] ` <33307c790712110813h23def95dvd068b7226e9fcd36@mail.gmail.com>
2007-12-11 20:37   ` 2.6.24-rc4-mm1 Andrew Morton
2007-12-11 21:20     ` 2.6.24-rc4-mm1 Ingo Molnar
2007-12-11 21:26     ` 2.6.24-rc4-mm1 Kok, Auke
2007-12-11 21:59       ` 2.6.24-rc4-mm1 Kok, Auke
2007-12-11 22:10       ` 2.6.24-rc4-mm1 Andrew Morton
2007-12-11 22:17         ` 2.6.24-rc4-mm1 Kok, Auke
2007-12-11 23:15           ` 2.6.24-rc4-mm1 Randy Dunlap
2007-12-12  4:16 ` 2.6.24-rc4-mm1 Rik van Riel
2007-12-13 17:45 ` 2.6.24-rc4-mm1 - BUG in tcp_fragment Cedric Le Goater
2007-12-13 23:00   ` Ilpo Järvinen
2007-12-14  6:52     ` Cedric Le Goater
2007-12-14 20:14     ` [PATCH net-2.6.25] Revert recent TCP work Ilpo Järvinen
2007-12-16 22:21       ` David Miller

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