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Date: Tue, 16 Aug 2016 10:55:05 +0200
From: Richard Cochran <richardcochran@gmail.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rik van Riel <riel@redhat.com>, Jouni Malinen <jkmalinen@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        George Spelvin <linux@sciencehorizons.net>,
        Len Brown <lenb@kernel.org>, Josh Triplett <josh@joshtriplett.org>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [patch 4 14/22] timer: Switch to a non cascading wheel
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On Fri, Aug 12, 2016 at 12:14:11PM -0700, Paul E. McKenney wrote:
> FWIW, I do appear to be seeing more lost wakeups on current mainline
> than on v4.7, but not enough of a difference to get a reliable bisction
> in reasonable time.

We are seeing reproducible hangs* when running Steven's
stress-cpu-hotplug under kvm.  This hang goes back to v4.7 at least.
I couldn't reproduce this with bare metal.  Thomas thought it was a
virtualization issue, not related to the hotplug rework.  He is away
until next week.  Maybe he knows more to say...

To reproduce, run 

   while [ 1 ]; do ./stress-cpu-hotplug ; done

and wait about 20 minutes (or longer).

Thanks,
Richard

* INFO: task cpuhp/7:49 blocked for more than 120 seconds