linux-kernel - Re: [PATCH 4/6] watchdog: Boot-disable by default on full dynticks

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Message-ID: <20130613131057.GA15997@somewhere>
Date:	Thu, 13 Jun 2013 15:10:59 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Anish Singh <anish198519851985@...il.com>
Subject: Re: [PATCH 4/6] watchdog: Boot-disable by default on full dynticks

On Wed, Jun 12, 2013 at 01:03:16PM -0400, Don Zickus wrote:
> On Wed, Jun 12, 2013 at 04:02:36PM +0200, Frederic Weisbecker wrote:
> > When the watchdog runs, it prevents the full dynticks
> > CPUs from stopping their tick because the hard lockup
> > detector uses perf events internally, which in turn
> > rely on the periodic tick.
> > 
> > Since this is a rather confusing behaviour that is not
> > easy to track down and identify for those who want to
> > test CONFIG_NO_HZ_FULL, let's default disable the
> > watchdog on boot time when full dynticks is enabled.
> > 
> > The user can still enable it later on runtime using
> > proc or sysctl.
> 
> I thought we had a conversation awhile ago, where we agreed this was going
> to be fixed for 3.11?  Didn't Peter find the patch and apply it to his
> tree?  I am confused why this is still needed?

We agreed on the patch but it hasn't been applied yet. I'm trying to get
a sane series of nohz patches before sending to Ingo.

Thanks.
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