[V4,3/3] time/cpuidle:Handle failed call to BROADCAST_ENTER on archs with CPUIDLE_FLAG_TIMER_STOP set

Some archs set the CPUIDLE_FLAG_TIMER_STOP flag for idle states in which the
local timers stop. The cpuidle_idle_call() currently handles such idle states
by calling into the broadcast framework so as to wakeup CPUs at their next
wakeup event. With the hrtimer mode of broadcast, the BROADCAST_ENTER call
into the broadcast frameowork can fail for archs that do not have an external
clock device to handle wakeups and the CPU in question has to thus be made
the stand by CPU. This patch handles such cases by failing the call into
cpuidle so that the arch can take some default action. The arch will certainly
not enter a similar idle state because a failed cpuidle call will also implicitly
indicate that the broadcast framework has not registered this CPU to be woken up.
Hence we are safe if we fail the cpuidle call.

In the process move the functions that trace idle statistics just before and
after the entry and exit into idle states respectively. In other
scenarios where the call to cpuidle fails, we end up not tracing idle
entry and exit since a decision on an idle state could not be taken. Similarly
when the call to broadcast framework fails, we skip tracing idle statistics
because we are in no further position to take a decision on an alternative
idle state to enter into.

Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
---

 drivers/cpuidle/cpuidle.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

On Friday, February 07, 2014 01:36:52 PM Preeti U Murthy wrote:
> Some archs set the CPUIDLE_FLAG_TIMER_STOP flag for idle states in which the
> local timers stop. The cpuidle_idle_call() currently handles such idle states
> by calling into the broadcast framework so as to wakeup CPUs at their next
> wakeup event. With the hrtimer mode of broadcast, the BROADCAST_ENTER call
> into the broadcast frameowork can fail for archs that do not have an external
> clock device to handle wakeups and the CPU in question has to thus be made
> the stand by CPU. This patch handles such cases by failing the call into
> cpuidle so that the arch can take some default action. The arch will certainly
> not enter a similar idle state because a failed cpuidle call will also implicitly
> indicate that the broadcast framework has not registered this CPU to be woken up.
> Hence we are safe if we fail the cpuidle call.
> 
> In the process move the functions that trace idle statistics just before and
> after the entry and exit into idle states respectively. In other
> scenarios where the call to cpuidle fails, we end up not tracing idle
> entry and exit since a decision on an idle state could not be taken. Similarly
> when the call to broadcast framework fails, we skip tracing idle statistics
> because we are in no further position to take a decision on an alternative
> idle state to enter into.
> 
> Signed-off-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> 
>  drivers/cpuidle/cpuidle.c |   14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index a55e68f..8beb0f02 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -140,12 +140,14 @@ int cpuidle_idle_call(void)
>  		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 (broadcast &&
> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
> +		return -EBUSY;
> +
> +
> +	trace_cpu_idle_rcuidle(next_state, dev->cpu);
>  
>  	if (cpuidle_state_is_coupled(dev, drv, next_state))
>  		entered_state = cpuidle_enter_state_coupled(dev, drv,
> @@ -153,11 +155,11 @@ int cpuidle_idle_call(void)
>  	else
>  		entered_state = cpuidle_enter_state(dev, drv, next_state);
>  
> +	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> +
>  	if (broadcast)
>  		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
>  
> -	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);
> 
> --
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