linux-kernel - Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ

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Message-ID: <20130515175017.GS23604@redhat.com>
Date:	Wed, 15 May 2013 13:50:17 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ_FULL is
 enabled

On Wed, May 15, 2013 at 07:11:53PM +0200, Peter Zijlstra wrote:
> On Wed, May 15, 2013 at 06:59:15PM +0200, Peter Zijlstra wrote:
> > On Wed, May 15, 2013 at 11:27:02AM -0400, Steven Rostedt wrote:
> > > Right now perf requires a tick, not sure exactly why, but you can look
> > > at the code in perf_event_task_tick(). Thus if NO_HZ_FULL sees that a
> > > perf tick is pending, it won't disable ticks. Unfortunately, the
> > > watchdogs, both NMI and soft lockup, use the perf infrastructure to
> > > trigger NMIs or interrupts. This adds a perf element on the rotate list
> > > and keeps NO_HZ_FULL from *ever* activating.
> > > 
> > 
> > Hmm.. Stephane had a bunch of patches converting the rotation thing to
> > an hrtimer. I seem to have forgotten what happened to them but I can't
> > seem to find them merged.
> > 
> > I'll go look.
> > 
> > That leaves the frequency stuff, but the watchdog doesn't use that.
> > 
> > At which point we could run the watchdog without perf_event_task_tick().
> 
> Found them:
> 
> 1364991694-5876-1-git-send-email-eranian@...gle.com
> 
> Looks like they were stuck in my inbox and never applied, so I just did.
> They should appear in tip soonish.

That was easy.  Next problem! :-p

Thanks Peter!

Cheers,
Don

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