From: paulmck@linux.vnet.ibm.com (Paul E. McKenney)
To: linux-arm-kernel@lists.infradead.org
Subject: rcu self-detected stall messages on OMAP3, 4 boards
Date: Sat, 22 Sep 2012 16:17:33 -0700 [thread overview]
Message-ID: <20120922231733.GI2934@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1209222214120.22590@utopia.booyaka.com>
On Sat, Sep 22, 2012 at 10:20:19PM +0000, Paul Walmsley wrote:
> Hi Paul
>
> On Sat, 22 Sep 2012, Paul E. McKenney wrote:
>
> > Strangely enough, I believe that I have inadvertently fixed this in
> > my -rcu tree:
> >
> > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/next
> >
> > Nevertheless, if you get a chance to try it, I would be interested to
> > hear if my guess is correct.
>
> Yes, good news: the stall warnings go away with that branch.
Very good!
> > The trick is that a kthread drives the grace period in -rcu, regardless
> > of whether or not there are callbacks.
>
> This is "rcu: Move quiescent-state forcing into kthread" ?
Yep, plus the preceding commits moving grace-period initialization and
cleanup into that same kthread. This was motivated by a bug report
last February complaining about 200-microsecond latency spikes from
RCU grace-period initialization. On systems with 4096 CPUs.
Real-time response. It is far bigger than I thought. ;-)
> Added some debugging into rcu_gp_kthread() after that commit and can
> confirm that the quiescent-state forcing loop does start a few times when
> there are zero callbacks pending (modulo any races in my measurement
> code).
Cool, thank you! Assuming it works, that indicates that there is long-term
value to the fix for this problem. On larger systems, extra grace periods
are not what you want, as their expense increases with the number of CPUs.
> > However, the backport would not be something that -stable would be happy
> > with, so I will be putting together a fix for mainline. This thing
> > has been in the kernel since about 2004, not sure why you didn't hit
> > it earlier.
>
> One other data point in that regard - noticed the warnings don't appear
> when the board is booted with:
>
> commit 4fa3b6cb1bc8c14b81b4c8ffdfd3f2500a7e9367
> Author: Paul E. McKenney <paul.mckenney@linaro.org>
> Date: Tue Jun 5 15:53:53 2012 -0700
>
> rcu: Fix qlen_lazy breakage
You lost me on this one. This is already in mainline, so if you were
using (say) 3.6-rc6, you would already have this commit applied.
Thanx, Paul
next prev parent reply other threads:[~2012-09-22 23:17 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-12 22:51 rcu self-detected stall messages on OMAP3, 4 boards Paul Walmsley
2012-09-13 1:12 ` Paul E. McKenney
2012-09-13 18:52 ` Paul Walmsley
2012-09-20 0:03 ` Paul E. McKenney
2012-09-20 7:56 ` Paul Walmsley
2012-09-20 15:03 ` Bruce, Becky
2012-09-20 21:49 ` Bruce, Becky
2012-09-20 22:01 ` Paul E. McKenney
2012-09-20 22:47 ` Paul Walmsley
2012-09-20 23:21 ` Paul E. McKenney
2012-09-21 18:08 ` Paul Walmsley
2012-09-21 18:58 ` Paul E. McKenney
2012-09-21 19:11 ` Paul Walmsley
2012-09-21 19:57 ` Paul E. McKenney
2012-09-21 20:31 ` Tony Lindgren
2012-09-21 22:03 ` Paul E. McKenney
2012-09-22 15:45 ` Frederic Weisbecker
2012-09-22 16:00 ` Paul E. McKenney
2012-09-21 22:12 ` Paul E. McKenney
2012-09-22 18:42 ` Paul Walmsley
2012-09-22 20:10 ` Paul E. McKenney
2012-09-22 21:59 ` Paul E. McKenney
2012-09-22 22:25 ` Paul Walmsley
2012-09-22 23:11 ` Paul E. McKenney
2012-09-23 7:55 ` Paul Walmsley
2012-09-23 12:11 ` Paul E. McKenney
2012-09-23 1:42 ` Paul Walmsley
2012-09-23 1:56 ` Paul E. McKenney
2012-09-23 2:01 ` Paul Walmsley
2012-09-24 9:41 ` Shilimkar, Santosh
2012-09-24 13:18 ` Paul E. McKenney
2012-10-01 8:55 ` Linus Walleij
2012-10-01 13:28 ` Paul E. McKenney
2012-09-21 18:59 ` Paul Walmsley
2012-09-21 17:47 ` Paul Walmsley
2012-09-21 17:51 ` Paul Walmsley
2012-09-21 21:20 ` Paul E. McKenney
2012-09-21 22:41 ` Paul Walmsley
2012-09-22 0:05 ` Paul E. McKenney
2012-09-22 18:16 ` Paul Walmsley
2012-09-22 19:52 ` Paul E. McKenney
2012-09-22 22:20 ` Paul Walmsley
2012-09-22 23:17 ` Paul E. McKenney [this message]
2012-09-24 21:54 ` Paul Walmsley
2012-09-24 22:00 ` Paul E. McKenney
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