Re: [RFC][PATCH 8/8] sched,idle: Reflow cpuidle_idle_call()

[Nicolas Pitre]

On Fri, 11 Apr 2014, Peter Zijlstra wrote:

> Apply goto to reduce lines and nesting levels.
> 
> Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> ---
>  kernel/sched/idle.c |  138 +++++++++++++++++++++++-----------------------------
>  1 file changed, 62 insertions(+), 76 deletions(-)
> 
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -73,7 +73,7 @@ static int cpuidle_idle_call(void)
>  {
>  	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
>  	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
> -	int next_state, entered_state, ret;
> +	int next_state, entered_state;
>  	bool broadcast;
>  
>  	/*
> @@ -102,90 +102,64 @@ static int cpuidle_idle_call(void)
>  	 * Check if the cpuidle framework is ready, otherwise fallback
>  	 * to the default arch specific idle method
>  	 */
> -	ret = cpuidle_enabled(drv, dev);
> +	if (cpuidle_enabled(drv, dev))
> +		goto use_default;

Why not using braces here and moving the use_default code block inside 
it instead?


>  
> -	if (!ret) {
> -		/*
> -		 * Ask the governor to choose an idle state it thinks
> -		 * it is convenient to go to. There is *always* a
> -		 * convenient idle state
> -		 */
> -		next_state = cpuidle_select(drv, dev);
> -
> -		/*
> -		 * The idle task must be scheduled, it is pointless to
> -		 * go to idle, just update no idle residency and get
> -		 * out of this function
> -		 */
> -		if (current_clr_polling_and_test()) {
> -			dev->last_residency = 0;
> -			entered_state = next_state;
> -			local_irq_enable();
> -		} else {
> -			broadcast = !!(drv->states[next_state].flags &
> -				       CPUIDLE_FLAG_TIMER_STOP);
> -
> -			if (broadcast) {
> -				/*
> -				 * Tell the time framework to switch
> -				 * to a broadcast timer because our
> -				 * local timer will be shutdown. If a
> -				 * local timer is used from another
> -				 * cpu as a broadcast timer, this call
> -				 * may fail if it is not available
> -				 */
> -				ret = clockevents_notify(
> -					CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
> -					&dev->cpu);
> -			}
> -
> -			if (!ret) {
> -				trace_cpu_idle_rcuidle(next_state, dev->cpu);
> -
> -				/*
> -				 * Enter the idle state previously
> -				 * returned by the governor
> -				 * decision. This function will block
> -				 * until an interrupt occurs and will
> -				 * take care of re-enabling the local
> -				 * interrupts
> -				 */
> -				entered_state = cpuidle_enter(drv, dev,
> -							      next_state);
> -
> -				trace_cpu_idle_rcuidle(PWR_EVENT_EXIT,
> -						       dev->cpu);
> -
> -				if (broadcast)
> -					clockevents_notify(
> -						CLOCK_EVT_NOTIFY_BROADCAST_EXIT,
> -						&dev->cpu);
> -
> -				/*
> -				 * Give the governor an opportunity to reflect on the
> -				 * outcome
> -				 */
> -				cpuidle_reflect(dev, entered_state);
> -			}
> -		}
> -	}
> +	/*
> +	 * Ask the governor to choose an idle state it thinks
> +	 * it is convenient to go to. There is *always* a
> +	 * convenient idle state
> +	 */
> +	next_state = cpuidle_select(drv, dev);
>  
>  	/*
> -	 * We can't use the cpuidle framework, let's use the default
> -	 * idle routine
> +	 * The idle task must be scheduled, it is pointless to
> +	 * go to idle, just update no idle residency and get
> +	 * out of this function
>  	 */
> -	if (ret) {
> -		if (!current_clr_polling_and_test())
> -			arch_cpu_idle();
> -		else
> -			local_irq_enable();
> +	if (current_clr_polling_and_test()) {
> +		dev->last_residency = 0;
> +		entered_state = next_state;
> +		local_irq_enable();
> +		goto exit_idle;
>  	}
>  
> +	broadcast = !!(drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP);
> +
> +	/*
> +	 * Tell the time framework to switch to a broadcast timer
> +	 * because our local timer will be shutdown. If a local timer
> +	 * is used from another cpu as a broadcast timer, this call may
> +	 * fail if it is not available
> +	 */
> +	if (broadcast &&
> +	    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
> +		goto use_default;
> +
> +	trace_cpu_idle_rcuidle(next_state, dev->cpu);
> +
> +	/*
> +	 * Enter the idle state previously returned by the governor decision.
> +	 * This function will block until an interrupt occurs and will take
> +	 * care of re-enabling the local interrupts
> +	 */
> +	entered_state = cpuidle_enter(drv, dev, next_state);
> +
> +	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> +
> +	if (broadcast)
> +		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
> +
> +	/*
> +	 * Give the governor an opportunity to reflect on the outcome
> +	 */
> +	cpuidle_reflect(dev, entered_state);
> +
> +exit_idle:
>  	__current_set_polling();
>  
>  	/*
> -	 * It is up to the idle functions to enable back the local
> -	 * interrupt
> +	 * It is up to the idle functions to reenable local interrupts
>  	 */
>  	if (WARN_ON_ONCE(irqs_disabled()))
>  		local_irq_enable();
> @@ -194,6 +168,18 @@ static int cpuidle_idle_call(void)
>  	start_critical_timings();
>  
>  	return 0;
> +
> +	/*
> +	 * We can't use the cpuidle framework, let's use the default idle
> +	 * routine
> +	 */
> +use_default:
> +	if (current_clr_polling_and_test())
> +		local_irq_enable();
> +	else
> +		arch_cpu_idle();
> +
> +	goto exit_idle;
>  }
>  
>  /*
> 
> 
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