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SubjectRe: [PATCH V2 4/5] idle: Move idle conditions in cpuidle_idle main function
On 02/24/2014 05:05 PM, Peter Zijlstra wrote:
> On Mon, Feb 24, 2014 at 04:39:08PM +0100, Daniel Lezcano wrote:
>
>>> And when you do that; you can also push down the
>>> current_clr_polling_and_test() muck so it doesn't cover the actual
>>> cpuidle policy code.
>>
>> I am not getting it. Where do you suggest to move it ?
>
> A little something like so I suppose;

Thanks for taking the time to send me this patch.

> only call
> current_clr_polling_and_test() right before calling the actual idle
> function. Although I suppose cpuidle_enter() can still do all sorts of
> weird.

Well there is the polling idle state for the x86 and ppc cpuidle
drivers. Except that, I think we have something more or less clean.

> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -78,37 +78,35 @@ static int cpuidle_idle_call(void)
> stop_critical_timings();
> rcu_idle_enter();
>
> - next_state = cpuidle_enabled(drv, dev);
> - if (next_state < 0) {
> - arch_cpu_idle();
> - goto out;
> - }
> -
> - /*
> - * Ask the governor for the next state, this call can fail for
> - * different reasons: cpuidle is not enabled or an idle state
> - * fulfilling the constraints was not found. In this case, we
> - * fall back to the default idle function
> - */
> - next_state = cpuidle_select(drv, dev);
> + if (cpuidle_enabled(drv, dev) == 0) {
> + /*
> + * Ask the governor for the next state, this call can fail for
> + * different reasons: cpuidle is not enabled or an idle state
> + * fulfilling the constraints was not found. In this case, we
> + * fall back to the default idle function
> + */
> + next_state = cpuidle_select(drv, dev);
> +
> + if (current_clr_polling_and_test()) {
> + dev->last_residency = 0;
> + entered_state = next_state;
> + local_irq_enable();
> + } else {
> + trace_cpu_idle_rcuidle(next_state, dev->cpu);
> + entered_state = cpuidle_enter(drv, dev, next_state);
> + trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> + }
>
> - if (need_resched()) {

Ok. The need_resched is now replaced by 'current_clr_polling_and_test',
with a call to '__current_set_polling()' to set the flag back, right ?

For my personal information, what is the subtlety with:

if (tif_need_resched())
set_preempt_need_resched();

?

> - dev->last_residency = 0;
> /* give the governor an opportunity to reflect on the outcome */
> - cpuidle_reflect(dev, next_state);
> - local_irq_enable();
> - goto out;
> + cpuidle_reflect(dev, entered_state);
> + } else {
> + if (current_clr_polling_and_test())
> + local_irq_enable();
> + else
> + arch_cpu_idle();
> }
> + __current_set_polling();
>
> - trace_cpu_idle_rcuidle(next_state, dev->cpu);
> -
> - entered_state = cpuidle_enter(drv, dev, next_state);
> -
> - trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> -
> - /* give the governor an opportunity to reflect on the outcome */
> - cpuidle_reflect(dev, entered_state);
> -out:
> if (WARN_ON_ONCE(irqs_disabled()))
> local_irq_enable();
>
> @@ -145,16 +143,11 @@ static void cpu_idle_loop(void)
> * know that the IPI is going to arrive right
> * away
> */
> - if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
> + if (cpu_idle_force_poll || tick_check_broadcast_expired())
> cpu_idle_poll();
> - } else {
> - if (!current_clr_polling_and_test()) {
> - cpuidle_idle_call();
> - } else {
> - local_irq_enable();
> - }
> - __current_set_polling();
> - }
> + else
> + cpu_idle_call();
> +
> arch_cpu_idle_exit();
> /*
> * We need to test and propagate the TIF_NEED_RESCHED
>


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