linux-kernel - Re: [patch 4 14/22] timer: Switch to a non cascading wheel

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Message-ID: <20160816085505.GB23077@localhost.localdomain>
Date:	Tue, 16 Aug 2016 10:55:05 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Rik van Riel <riel@...hat.com>,
	Jouni Malinen <jkmalinen@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Mason <clm@...com>,
	Arjan van de Ven <arjan@...radead.org>, rt@...utronix.de,
	George Spelvin <linux@...encehorizons.net>,
	Len Brown <lenb@...nel.org>,
	Josh Triplett <josh@...htriplett.org>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [patch 4 14/22] timer: Switch to a non cascading wheel

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