linux-kernel - Re: [PATCH 3/5] idle: Reorganize the idle loop

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Date:	Tue, 11 Feb 2014 12:36:44 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
cc:	mingo@...nel.org, peterz@...radead.org, tglx@...utronix.de,
	rjw@...ysocki.net, preeti@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] idle: Reorganize the idle loop

On Tue, 11 Feb 2014, Daniel Lezcano wrote:

> Now that we have the main cpuidle function in idle.c, move some code from
> the idle mainloop to this function for the sake of clarity.
> 
> That removes if then else indentation difficult to follow when looking at the
> code. This patch does not the change the current behavior.

s/the change/change/

> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
> ---
>  include/linux/cpuidle.h |    2 ++
>  kernel/sched/idle.c     |   39 ++++++++++++++++++++-------------------
>  2 files changed, 22 insertions(+), 19 deletions(-)
> 
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 0befaff..a8d5bd3 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -175,6 +175,8 @@ static inline int cpuidle_enable_device(struct cpuidle_device *dev)
>  {return -ENODEV; }
>  static inline void cpuidle_disable_device(struct cpuidle_device *dev) { }
>  static inline int cpuidle_play_dead(void) {return -ENODEV; }
> +static inline struct cpuidle_driver *cpuidle_get_cpu_driver(
> +	struct cpuidle_device *dev) {return NULL; }
>  #endif
>  
>  #ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 6963822..8b10891 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -63,7 +63,6 @@ void __weak arch_cpu_idle(void)
>  	local_irq_enable();
>  }
>  
> -#ifdef CONFIG_CPU_IDLE
>  /**
>   * cpuidle_idle_call - the main idle function
>   *
> @@ -76,17 +75,26 @@ static int cpuidle_idle_call(void)
>  	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
>  	int next_state, entered_state;
>  
> -	/* ask the governor for the next state */
> +	stop_critical_timings();
> +	rcu_idle_enter();
> +
> +	/* 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
> +	 */

Preferred style for multi-line comment blocks is:

	/*
	 * First line here, leaving the opening line empty.
	 * Next line.
	 */

Otherwise...

Acked-by: Nicolas Pitre <nico@...aro.org>

>  	next_state = cpuidle_select(drv, dev);
> -	if (next_state < 0)
> -		return next_state;
> +	if (next_state < 0) {
> +		arch_cpu_idle();
> +		goto out;
> +	}
>  
>  	if (need_resched()) {
>  		dev->last_residency = 0;
>  		/* give the governor an opportunity to reflect on the outcome */
>  		cpuidle_reflect(dev, next_state);
>  		local_irq_enable();
> -		return 0;
> +		goto out;
>  	}
>  
>  	trace_cpu_idle_rcuidle(next_state, dev->cpu);
> @@ -97,15 +105,15 @@ static int cpuidle_idle_call(void)
>  
>  	/* 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();
> +
> +	rcu_idle_exit();
> +	start_critical_timings();
>  
>  	return 0;
>  }
> -#else
> -static inline int cpuidle_idle_call(void)
> -{
> -	return -ENODEV;
> -}
> -#endif
>  
>  /*
>   * Generic idle loop implementation
> @@ -138,14 +146,7 @@ static void cpu_idle_loop(void)
>  				cpu_idle_poll();
>  			} else {
>  				if (!current_clr_polling_and_test()) {
> -					stop_critical_timings();
> -					rcu_idle_enter();
> -					if (cpuidle_idle_call())
> -						arch_cpu_idle();
> -					if (WARN_ON_ONCE(irqs_disabled()))
> -						local_irq_enable();
> -					rcu_idle_exit();
> -					start_critical_timings();
> +					cpuidle_idle_call();
>  				} else {
>  					local_irq_enable();
>  				}
> -- 
> 1.7.9.5
> 
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