On Tue, 2015-03-17 at 02:53 +0100, Mike Galbraith wrote:

On Mon, 2015-03-16 at 21:24 +0100, Sebastian Andrzej Siewior wrote:

quoted

What you do is that you accept the fact that the timer-softirq is
scheduled for no reason and then you try to disable the tick from within
the timer-softirq. I assumed that it would work get the "expired timer"
somehow.

Yup, it works around that otherwise crippling wakeup.  If I re-apply..

     timers-do-not-raise-softirq-unconditionally.patch

..the workaround is not needed of course, but the livelock fix still is.
I haven't yet tested that in 3.18-rt though, only 4.0-rt, but I presume
it'll be the same deal there when I do.

Did that, and it is.  Fire up tbench 4 + make -j4 on my i7-4790+smt box
booted nohz_full=2,3,6,7, death spiral begins shortly thereafter.

	-Mike