On Thu, 2015-03-12 at 11:09 -0400, Steven Rostedt wrote:
> On Thu, 12 Mar 2015 10:38:13 +0100
> Mike Galbraith <umgwanakikbuti@xxxxxxxxx> wrote:
>
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -783,12 +783,16 @@ static inline bool got_nohz_idle_kick(vo
> > #ifdef CONFIG_NO_HZ_FULL
> > bool sched_can_stop_tick(void)
> > {
> > + int softirqd = IS_ENABLED(CONFIG_PREEMPT_RT_FULL);
> > +
> > + softirqd &= current == this_cpu_ksoftirqd();
>
> Ug, binary and logical ANDs should not be combined. Just looks nasty.
> What about:
>
> softirqd = !!(IS_ENABLED(CONFIG_PREEMPT_RT_FULL) &&
> current == this_cpu_ksoftirqd());
My way looks prettier to me, but I seem to be the only who thinks so
(this is not the first time it got a gripe), so I'll change it ;-)
> > +
> > /*
> > * More than one running task need preemption.
> > * nr_running update is assumed to be visible
> > * after IPI is sent from wakers.
> > */
> > - if (this_rq()->nr_running > 1)
> > + if (this_rq()->nr_running - softirqd > 1)
>
> There should also be a comment explaining this hack.
Yeah.
> > --- a/kernel/time/tick-sched.c
> > +++ b/kernel/time/tick-sched.c
> > @@ -222,7 +222,14 @@ void __tick_nohz_full_check(void)
> >
> > static void nohz_full_kick_work_func(struct irq_work *work)
> > {
> > + unsigned long flags;
> > +
> > + local_save_flags(flags);
> > + /* ksoftirqd processes softirqs with interrupts enabled */
> > + if (current == this_cpu_ksoftirqd())
> > + local_irq_disable();
>
> Why the funkiness above? Why not just call local_irq_save()?
Gone. It would be good to make the rest gone too, it's ain't pretty it
just works.
-Mike
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