Re: [PATCH 1/5] idle/cpuidle: Split cpuidle_idle_call main function into smaller functions

[Daniel Lezcano]

On 02/12/2014 11:38 AM, Preeti U Murthy wrote:
> Hi Daniel,
>
> On 02/11/2014 08:41 PM, Daniel Lezcano wrote:
> > 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@xxxxxxxxxx>
> > ---
> >   drivers/cpuidle/cpuidle.c |  102 ++++++++++++++++++++++++++++++++-------------
> >   include/linux/cpuidle.h   |   14 +++++++
> >   2 files changed, 87 insertions(+), 29 deletions(-)
> >
> > diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> > index a55e68f..172ab6a 100644
> > --- a/drivers/cpuidle/cpuidle.c
> > +++ b/drivers/cpuidle/cpuidle.c
> > @@ -108,6 +108,71 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
> >   }
> >
> >   /**
> > + * 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. On error it returns:
> > + * -NODEV : the cpuidle framework is not available
> > + * -EBUSY : the cpuidle framework is not initialized
> > + */
> > +int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> > +{
> > +	if (off || !initialized)
> > +		return -ENODEV;
> > +
> > +	if (!drv || !dev || !dev->enabled)
> > +		return -EBUSY;
>
> I would suggest moving the above two conditions under another function,
> cpuidle_enabled() maybe? The reason is, cpuidle_select() indicates that,
> it is invoked to select an idle state. While you are expecting this
> function to return an idle state, it seems counter-intuitive to return a
> ENODEV/EBUSY. This function is expected to be a call into the governor
> specific code and the same function should not be used to verify if
> cpuidle is enabled/not IMHO.

Yes, I fully agree. I will fix that.

> > +
> > +	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);
>
> The tip tree, timers/core branch has the patch,
> tick: Introduce hrtimer based broadcast. In the problem scenario that
> this patchset is addressing, the call to broadcast framework may return
> an error indicating that the idle state in question cannot be entered
> into. I wanted to bring it to your notice, so that early on you can take
> care of this. You will need to add code below in the invocation of
> cpuidle_enter() to verify if the idle state was entered into or not. If
> it was not, then you will need to skip tracing and reflecting of the
> idle state and directly exit the cpuidle loop with a failed status.

Ok.

Thanks !


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