Re: rcu_sched stalls in idle task introduced in pre-4.8?

From	Rich Felker <dalias@libc.org>
Newsgroups	linux.kernel
Subject	Re: rcu_sched stalls in idle task introduced in pre-4.8?
Date	2016-09-09 00:20 +0200
Message-ID	<sffPQ-3bV-19@gated-at.bofh.it> (permalink)
References	(2 earlier) <s1Ny1-s4-3@gated-at.bofh.it> <s1ODM-16D-29@gated-at.bofh.it> <s1ODM-16D-27@gated-at.bofh.it> <s1ONs-19V-13@gated-at.bofh.it> <s2rF7-1SU-21@gated-at.bofh.it>
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On Wed, Aug 03, 2016 at 09:16:31AM -0700, Paul E. McKenney wrote:
> On Tue, Aug 02, 2016 at 01:45:04PM -0700, Paul E. McKenney wrote:
> > On Tue, Aug 02, 2016 at 04:32:17PM -0400, Rich Felker wrote:
> > > On Tue, Aug 02, 2016 at 12:48:02PM -0700, Paul E. McKenney wrote:
> 
> [ . . . ]
> 
> > > > Does the problem reproduces easily?
> > > 
> > > Yes, it happens right after boot and repeats every 30-90 seconds or
> > > so.
> > 
> > Well, that at least makes it easier to test any patches!
> > 
> > > > A bisection might be very helpful.
> > > 
> > > Bisection would require some manual work to setup because the whole
> > > reason I was rebasing on Linus's tree was to adapt the drivers to
> > > upstream infrastructure changes (the new cpuhp stuff replacing
> > > notifier for cpu starting). The unfortunate way it was done, each
> > > driver adds an enum to linux/cpuhotplug.h so all the patches have
> > > gratuitous conflicts. In addition, for older revisions in Linus's
> > > tree, there's at least one show-stopping (hang during boot) bug that
> > > needs a cherry-pick to fix. There may be other small issues too. I
> > > don't think they're at all insurmountible but it requires an annoying
> > > amount of scripting.
> > 
> > I had to ask!  Might eventually be necessary, but let's see what we
> > can learn from what you currently have.
> 
> And at first glance, my overnight run looks uglier than I would expect.
> I am now running tests at v4.7, and will run other tests to see if
> there really is a statistically significant degradation.  If there is,
> then I might be able to bisect, though with nine-hour runs this could
> take quite some time.

Any more thoughts on this? I'm testing v4.8-rc5 (plus jcore drivers
not yet upstream) and it's still happening.

Rich

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Re: rcu_sched stalls in idle task introduced in pre-4.8? Rich Felker <dalias@libc.org> - 2016-09-09 00:20 +0200
  Re: rcu_sched stalls in idle task introduced in pre-4.8? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-10 12:20 +0200
    Re: rcu_sched stalls in idle task introduced in pre-4.8? Rich Felker <dalias@libc.org> - 2016-09-12 17:20 +0200
      Re: rcu_sched stalls in idle task introduced in pre-4.8? "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-09-12 17:40 +0200

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