From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Vivek Goyal <vgoyal@redhat.com>
Cc: Paul Bolle <pebolle@tiscali.nl>, Jens Axboe <jaxboe@fusionio.com>,
linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: Mysterious CFQ crash and RCU
Date: Fri, 3 Jun 2011 08:33:44 -0700 [thread overview]
Message-ID: <20110603153344.GB2333@linux.vnet.ibm.com> (raw)
In-Reply-To: <20110603134514.GA31057@redhat.com>
On Fri, Jun 03, 2011 at 09:45:14AM -0400, Vivek Goyal wrote:
> On Thu, Jun 02, 2011 at 10:07:24PM -0700, Paul E. McKenney wrote:
>
> [..]
> > > Thu May 26 10:47:20 CEST 2011
> > > /sys/kernel/debug/rcu/rcugp:
> > > rcu_sched: completed=682249 gpnum=682250
> >
> > 15 more seconds, a few thousand more grace periods. About 500 grace
> > periods per second, which is quite reasonable on a single-CPU system.
>
> PaulB mentioned that crash happened at May 26 10:47:07. I am wondering
> how are we able to sample the data after the crash. I am assuming
> that above data gives information only before crash and does not
> tell us anything about what happened just before crash. What am I missing.
>
> PaulM, in one of the mails you had mentioned that one could print
> context switch id to make sure we did not block in rcu section. Would
> you have quick pointer where is context switch id stored. May be
> I can write a small patch for PaulB.
>From what I can see, the task_struct nvcsw and nivcsw fields should do
it, though I am not seeing where these are incremented.
So if these don't do what you need, the following (untested but trivial)
patch will provide an rcu_switch_count in the task structure.
Thanx, Paul
------------------------------------------------------------------------
rcu: add diagnostic per-task context-switch count
Note that this is also incremented by softirqs.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2a8621c..5ef22e2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1261,6 +1261,7 @@ struct task_struct {
#ifdef CONFIG_RCU_BOOST
struct rt_mutex *rcu_boost_mutex;
#endif /* #ifdef CONFIG_RCU_BOOST */
+ unsigned long rcu_switch_count;
#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
struct sched_info sched_info;
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 89419ff..080c6eb 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -154,6 +154,7 @@ void rcu_bh_qs(int cpu)
*/
void rcu_note_context_switch(int cpu)
{
+ current->rcu_switch_count++;
rcu_sched_qs(cpu);
rcu_preempt_note_context_switch(cpu);
}
next prev parent reply other threads:[~2011-06-03 15:33 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-19 22:24 Mysterious CFQ crash and RCU Vivek Goyal
2011-05-21 21:00 ` Paul E. McKenney
2011-05-21 22:23 ` Paul Bolle
2011-05-21 23:54 ` Paul E. McKenney
2011-05-22 19:30 ` Paul Bolle
2011-05-22 20:13 ` Paul E. McKenney
2011-05-23 15:21 ` Vivek Goyal
2011-05-23 15:38 ` Paul E. McKenney
2011-05-23 22:20 ` Paul Bolle
2011-05-24 4:14 ` Paul E. McKenney
2011-05-24 9:41 ` Jens Axboe
2011-05-24 14:35 ` Paul E. McKenney
2011-05-24 14:51 ` Jens Axboe
2011-05-24 15:42 ` Paul E. McKenney
2011-05-24 15:51 ` Paul E. McKenney
2011-05-25 8:28 ` Paul Bolle
2011-05-25 8:46 ` Jens Axboe
2011-05-25 9:13 ` Paul Bolle
2011-05-25 9:30 ` Jens Axboe
2011-05-25 9:40 ` Paul Bolle
2011-05-25 12:48 ` Paul Bolle
2011-05-25 12:51 ` Jens Axboe
2011-05-25 17:28 ` Paul Bolle
2011-05-25 18:59 ` Jens Axboe
2011-05-25 10:17 ` Paul Bolle
2011-05-25 15:33 ` Paul E. McKenney
2011-05-25 17:44 ` Paul Bolle
2011-05-25 20:40 ` Paul E. McKenney
2011-05-26 9:15 ` Paul Bolle
2011-06-03 5:07 ` Paul E. McKenney
2011-06-03 13:45 ` Vivek Goyal
2011-06-03 15:33 ` Paul E. McKenney [this message]
2011-06-03 16:54 ` Paul E. McKenney
2011-06-04 12:22 ` Paul Bolle
2011-06-04 12:50 ` Paul Bolle
2011-06-04 16:03 ` Paul E. McKenney
2011-06-04 22:48 ` Paul Bolle
2011-06-04 23:06 ` Paul E. McKenney
2011-08-04 15:05 ` Vivek Goyal
2011-08-04 19:43 ` Jens Axboe
2011-08-04 19:51 ` Vivek Goyal
2011-06-05 6:56 ` Jens Axboe
2011-06-05 8:39 ` Paul Bolle
2011-06-05 10:38 ` Paul Bolle
2011-06-05 22:51 ` Jens Axboe
2011-06-06 14:28 ` Vivek Goyal
2011-05-23 15:36 ` Vivek Goyal
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