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

[Peter Zijlstra]

On Wed, May 15, 2013 at 11:06:53AM -0400, Don Zickus wrote:
> Coming into the middle of the thread is always hard, but why/how does perf
> disable nohz_full?  I didn't think the hardware events of perf would cause
> problems as they are no different than an irq.  Curious.

Yah, right :-) So I think what happens is that when we enter kernel
space for whatever reason (say NMIs for a watchdog), we kill the magic
NO_HZ state that allows a single task that's stuck in userspace to
effectively have the tick disabled.

But yeah, the initial patch was a tad light on detail, so I'll have to
let Steve and Frederic expand / correct.
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