Re: [PATCH 1/2] nohz: Disable LOCKUP_DETECTOR when NO_HZ_FULL is enabled

[Don Zickus <dzickus@redhat.com>]

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@google.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