Re: [patch 05/34] idle: Implement generic idle function

Thomas Gleixner
2013-03-25T10:39:29Z

On Sat, 23 Mar 2013, Heiko Carstens wrote:

> On Thu, Mar 21, 2013 at 09:53:00PM -0000, Thomas Gleixner wrote:
> > All idle functions in arch/* are more or less the same, plus minus a
> > few bugs and extra instrumentation, tickless support and other
> > optional items.
> >
> > Implement a generic idle function which resembles the functionality
> > found in arch/. Provide weak arch_cpu_idle_* functions which can be
> > overridden by the architecture code if needed.
> >
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>
> [...]
>
> > +static void cpu_idle_loop(void)
> > +{
> > + while (1) {
> > + tick_nohz_idle_enter();
> > +
> > + while (!need_resched()) {
> > + check_pgt_cache();
> > + rmb();
> > +
> > + if (cpu_is_offline(smp_processor_id()))
> > + arch_cpu_idle_dead();
> > +
> > + local_irq_disable();
> > + arch_cpu_idle_enter();
> > +
> > + if (cpu_idle_force_poll) {
> > + cpu_idle_poll();
> > + } else {
> > + current_clr_polling();
> > + if (!need_resched()) {
> > + stop_critical_timings();
> > + rcu_idle_enter();
> > + arch_cpu_idle();
> > + WARN_ON_ONCE(!irqs_disabled());
>
> This should be WARN_ON_ONCE(irqs_disabled()), no?

Gah, yes.

> > + rcu_idle_exit();
> > + start_critical_timings();
> > + } else {
> > + local_irq_enable();
> > + }
> > + current_set_polling();
> > + }
> > + arch_cpu_idle_exit();
> > + }
> > + tick_nohz_idle_exit();
>
> I was wondering why the scheduler doesn't complain when being called with
> irqs disabled. In fact tick_nohz_idle_exit() enables irqs unconditionally
> iff CONFIG_NO_HZ is set.

It should complain. I'll have a look again.

> > + schedule_preempt_disabled();
> > + }
> > +}
> > +
> > +void cpu_startup_entry(enum cpuhp_state state)
> > +{
> > + current_set_polling();
> > + arch_cpu_idle_prepare();
> > + cpu_idle_loop();
> > +}
> > +#endif
>
>