On Sat, 2012-10-20 at 12:22 -0400, Frederic Weisbecker wrote:
> +       if (empty) {
> +               /*
> +                * If an IPI is requested, raise it right away. Otherwise wait
> +                * for the next tick unless it's stopped. Now if the arch uses
> +                * some other obscure way than IPI to raise an irq work, just raise
> +                * and don't think further.
> +                */
> +               if (ipi || !arch_irq_work_has_ipi() || tick_nohz_tick_stopped())
> +                       arch_irq_work_raise();
> +       }
>         preempt_enable();
>  } 

Doesn't this have a problem where we enqueue the first lazy and then one
with ipi? In that case it appears we won't send the IPI because the
queue wasn't empty.