[V2,1/5] idle/cpuidle: Split cpuidle_idle_call main function into smaller functions

In order to allow better integration between the cpuidle framework and the
scheduler, reducing the distance between these two sub-components will
facilitate this integration by moving part of the cpuidle code in the idle
task file and, because idle.c is in the sched directory, we have access to
the scheduler's private structures.

This patch splits the cpuidle_idle_call main entry function into 3 calls
to a newly added API:
 1. select the idle state
 2. enter the idle state
 3. reflect the idle state

The cpuidle_idle_call calls these three functions to implement the main
idle entry function.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
---

ChangeLog:

V2: 
    * splitted cpuidle_select error check into 'cpuidle_enabled' function

---
 drivers/cpuidle/cpuidle.c |  114 ++++++++++++++++++++++++++++++++++------------
 include/linux/cpuidle.h   |   19 +++++++
 2 files changed, 105 insertions(+), 28 deletions(-)

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On 02/24/2014 04:00 PM, Peter Zijlstra wrote:
>
>
> None of this actually applies :/ I'm having major conflicts in
> driveres/cpuidle/cpuidle.c.

Ok, except if I am missing something, the patchset is based on top of 
tip/sched/core (commit 6990566).

On 02/25/2014 04:47 AM, Preeti U Murthy wrote:
> Hi Daniel,
>
> On 02/24/2014 07:25 PM, Daniel Lezcano wrote:
>> ---
>>   drivers/cpuidle/cpuidle.c |  114 ++++++++++++++++++++++++++++++++++------------
>>   include/linux/cpuidle.h   |   19 +++++++
>>   2 files changed, 105 insertions(+), 28 deletions(-)
>>
>> Index: cpuidle-next/drivers/cpuidle/cpuidle.c
>> ===================================================================
>> --- cpuidle-next.orig/drivers/cpuidle/cpuidle.c
>> +++ cpuidle-next/drivers/cpuidle/cpuidle.c
>> @@ -65,6 +65,26 @@ int cpuidle_play_dead(void)
>>   }
>>
>>   /**
>> + * cpuidle_enabled - check if the cpuidle framework is ready
>> + * @dev: cpuidle device for this cpu
>> + * @drv: cpuidle driver for this cpu
>> + *
>> + * Return 0 on success, otherwise:
>> + * -NODEV : the cpuidle framework is not available
>> + * -EBUSY : the cpuidle framework is not initialized
>> + */
>> +int cpuidle_enabled(struct cpuidle_driver *drv, struct cpuidle_device *dev)
>> +{
>> +	if (off || !initialized)
>> +		return -ENODEV;
>> +
>> +	if (!drv || !dev || !dev->enabled)
>> +		return -EBUSY;
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>>    * cpuidle_enter_state - enter the state and update stats
>>    * @dev: cpuidle device for this cpu
>>    * @drv: cpuidle driver for this cpu
>> @@ -108,6 +128,63 @@ int cpuidle_enter_state(struct cpuidle_d
>>   }
>>
>>   /**
>> + * cpuidle_select - ask the cpuidle framework to choose an idle state
>> + *
>> + * @drv: the cpuidle driver
>> + * @dev: the cpuidle device
>> + *
>> + * Returns the index of the idle state.
>> + */
>> +int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
>> +{
>> +	return cpuidle_curr_governor->select(drv, dev);
>> +}
>> +
>> +/**
>> + * cpuidle_enter - enter into the specified idle state
>> + *
>> + * @drv:   the cpuidle driver tied with the cpu
>> + * @dev:   the cpuidle device
>> + * @index: the index in the idle state table
>> + *
>> + * Returns the index in the idle state, < 0 in case of error.
>> + * The error code depends on the backend driver
>> + */
>> +int cpuidle_enter(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>> +		  int index)
>> +{
>> +	int entered_state;
>> +	bool broadcast = !!(drv->states[index].flags & CPUIDLE_FLAG_TIMER_STOP);
>> +
>> +	if (broadcast)
>> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
>> +
>> +	if (cpuidle_state_is_coupled(dev, drv, index))
>> +		entered_state = cpuidle_enter_state_coupled(dev, drv, index);
>> +	else
>> +		entered_state = cpuidle_enter_state(dev, drv, index);
>> +
>> +	if (broadcast)
>> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
>> +
>> +	return entered_state;
>> +}
>> +
>> +/**
>> + * cpuidle_reflect - tell the underlying governor what was the state
>> + * we were in
>> + *
>> + * @dev  : the cpuidle device
>> + * @index: the index in the idle state table
>> + *
>> + */
>> +void cpuidle_reflect(struct cpuidle_device *dev, int index)
>> +{
>> +	if (cpuidle_curr_governor->reflect)
>> +		cpuidle_curr_governor->reflect(dev, index);
>> +}
>> +
>> +/**
>>    * cpuidle_idle_call - the main idle loop
>>    *
>>    * NOTE: no locks or semaphores should be used here
>> @@ -116,51 +193,32 @@ int cpuidle_enter_state(struct cpuidle_d
>>   int cpuidle_idle_call(void)
>>   {
>>   	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
>> -	struct cpuidle_driver *drv;
>> +	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
>>   	int next_state, entered_state;
>> -	bool broadcast;
>>
>> -	if (off || !initialized)
>> -		return -ENODEV;
>> -
>> -	/* check if the device is ready */
>> -	if (!dev || !dev->enabled)
>> -		return -EBUSY;
>> -
>> -	drv = cpuidle_get_cpu_driver(dev);
>> +	next_state = cpuidle_enabled(drv, dev);
>
> Accepting the return of cpuidle_enabled() into a parameter named
> "next_state" looks misleading. You are not returning any idle state. You
> could use ret/enabled to accept the return value here perhaps?

Yes, it was to save an extra variable. I can replace it by a 'ret'.

>> +	if (next_state < 0)
>> +		return next_state;
>>
>>   	/* ask the governor for the next state */
>> -	next_state = cpuidle_curr_governor->select(drv, dev);
>> +	next_state = cpuidle_select(drv, dev);
>> +
>>   	if (need_resched()) {
>>   		dev->last_residency = 0;
>>   		/* give the governor an opportunity to reflect on the outcome */
>> -		if (cpuidle_curr_governor->reflect)
>> -			cpuidle_curr_governor->reflect(dev, next_state);
>> +		cpuidle_reflect(dev, next_state);
>>   		local_irq_enable();
>>   		return 0;
>>   	}
>>
>>   	trace_cpu_idle_rcuidle(next_state, dev->cpu);
>>
>> -	broadcast = !!(drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP);
>> -
>> -	if (broadcast)
>> -		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu);
>> -
>> -	if (cpuidle_state_is_coupled(dev, drv, next_state))
>> -		entered_state = cpuidle_enter_state_coupled(dev, drv,
>> -							    next_state);
>> -	else
>> -		entered_state = cpuidle_enter_state(dev, drv, next_state);
>> -
>> -	if (broadcast)
>> -		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
>> +	entered_state = cpuidle_enter(drv, dev, next_state);
>
> Shouldn't the return value be checked here, considering you are
> expecting the driver to return an error code. Another reason I mention
> this is that since you would have done BROADCAST_ENTRY and if this call
> to the broadcast framework succeeds, you will have to do a
> BROADCAST_EXIT irrespective of if the driver could put the CPU to that
> idle state or not. So even if cpuidle_enter() fails, you will need to do
> a clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu),
> although you will have to skip over cpuidle_reflect().
>
> So are there drivers which can return an error code when we call into
> the enter function of the idle states?

Except for the acpi noodle plate driver, no backend driver is returning 
an error.

> If not, you can probably avoid
> checking the error code return value of cpuidle_enter() altogether and
> make it simpler. Its not being checked in the current code too.

Yeah, that is the point. I don't want to mix the changes with this 
patchset. I agree, the code must be fixed but I prefer to do that in a 
separate patch.

Thanks for the review

   -- Daniel

>
> Thanks
>
> Regards
> Preeti U Murthy
>>
>>   	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
>>
>>   	/* give the governor an opportunity to reflect on the outcome */
>> -	if (cpuidle_curr_governor->reflect)
>> -		cpuidle_curr_governor->reflect(dev, entered_state);
>> +	cpuidle_reflect(dev, entered_state);
>>
>>   	return 0;
>>   }
>