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SubjectRe: rcu_sched stalls in idle task introduced in pre-4.8?
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.

Thanx, Paul

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