On Fri, Dec 22, 2017 at 03:51:13PM +0100, Thomas Gleixner wrote: > The conditions in irq_exit() to invoke tick_nohz_irq_exit() are: > > if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu)) > > This is too permissive in various aspects: > > 1) If need_resched() is set, then the tick cannot be stopped whether > the CPU is idle or in nohz full mode.
That's not exactly true. In nohz full mode the tick is not restarted on the switch from idle to a single task. And if an idle interrupt wakes up a single task and enqueues a timer, we want that timer to be programmed even though we have need_resched().
