On Tue, Dec 16, 2014 at 10:21:27PM +0100, Thomas Gleixner wrote:
> DEFINE_PER_CPU(nohz_full_must_tick, unsigned long);
>
> enum {
> NOHZ_SCHED_NEEDS_TICK,
> NOHZ_POSIXTIMER_NEEDS_TICK,
> NOHZ_PERF_NEEEDS_TICK,
> };
>
> /* rq->lock is held for evaluating rq->nr_running */
> static void sched_ttwu_nohz(struct rq *rq)
> {
> if (nohz_full_disabled())
> return;
>
> if (rq->nr_running != 2)
> return;
> set_bit(NOHZ_SCHED_NEEDS_TICK, this_cpu_ptr(nohz_full_must_tick);
> }
>
> /* rq->lock is held for evaluating rq->nr_running */
> static void sched_ttwu_remote_nohz(struct rq *rq)
> {
> if (nohz_full_disabled())
> return;
>
> if (rq->nr_running != 2)
> return;
> /*
> * Force smp_send_reschedule(). irq_exit() on the
> * remote cpu will handle the rest.
> */
smp_send_reschedule() is magic and does not guarantee irq_{enter,exit}()
being called, although we could audit and fix that.
> set_bit(NOHZ_SCHED_NEEDS_TICK, per_cpu_ptr(nohz_full_must_tick,
> rq->cpu);
> rq->force_send_resched = true;
> }
I'd make that force_send_resched the return value or so..
> /* rq->lock is held for evaluating rq->nr_running */
> static void sched_out_nohz(struct rq *rq)
> {
> if (nohz_full_disabled())
> return;
>
> if (rq->nr_running >= 2)
> return;
> clear_bit(NOHZ_SCHED_NEEDS_TICK, this_cpu_ptr(nohz_full_must_tick);
> }
>
> /* preeemption is disabled */
> static void sched_in_nohz(struct task_struct *task)
> {
> if (nohz_full_disabled())
> return;
>
> if (!task_uses_posix_timers(task))
> clear_bit(NOHZ_POSIXTIMER_NEEDS_TICK,
> this_cpu_ptr(nohz_full_must_tick));
> else
> set_bit(NOHZ_POSIXTIMER_NEEDS_TICK,
> this_cpu_ptr(nohz_full_must_tick));
>
/me hands you a few spare {} :-)
Arguably test state before doing a possibly pointless update?
> local_irq_disable();
> tick_full_nohz_update_state();
> local_irq_enable();
> }
But yes, that should work just fine..
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