On Wed, Jun 4, 2014 at 12:53 AM, Peter Zijlstra <pet...@infradead.org> wrote: > On Tue, Jun 03, 2014 at 05:29:50PM -0700, Andy Lutomirski wrote: >> @@ -229,6 +234,8 @@ static void cpu_idle_loop(void) >> */ >> preempt_set_need_resched(); >> tick_nohz_idle_exit(); >> + __current_clr_polling(); >> + smp_mb__after_clear_bit(); > > barriers always need a comment, and I'm not entirely sure why you put > this one here.
Will do. I actually suspect that the barrier isn't needed in this patch, but it will be needed one patch later when there's a sched_ttwu_pending after the barrier. I'll move this to the next patch and add a comment. The reason that the barrier is needed is that polling needs to be visibly cleared before checking for queued ttwu tasks, because otherwise another CPU could queue a ttwu task, do set_nr_if_polling, and get a true return value *after* sched_ttwu_pending because the CPU decided to defer the clear_bit. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
