Re: [v4 PATCH 1/5]: cpuidle: Cleanup drivers/cpuidle/cpuidle.c

[Balbir Singh <balbir@linux.vnet.ibm.com>]

* Arun R B <arun@linux.vnet.ibm.com> [2009-09-01 17:08:40]:

> * Arun R Bharadwaj <arun@linux.vnet.ibm.com> [2009-09-01 17:07:04]:
> 
> Cleanup drivers/cpuidle/cpuidle.c
> 
> Cpuidle maintains a pm_idle_old void pointer because, currently in x86
> there is no clean way of registering and unregistering a idle function.
>
> So remove pm_idle_old and leave the responsibility of maintaining the
> list of registered idle loops to the architecture specific code. If the
> architecture registers cpuidle_idle_call as its idle loop, only then
> this loop is called.
> 

It sounds as if there is a side-effect of this
patch on x86 (am I reading it incorrectly), which can be fixed, but
it will need a patch or so to get back the old behaviour on x86.
 
> Also remove unwanted functions cpuidle_[un]install_idle_handler,
> cpuidle_kick_cpus()
>
> Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com>
> ---
>  drivers/cpuidle/cpuidle.c  |   51 +++++++++++++++------------------------------
>  drivers/cpuidle/governor.c |    3 --
>  2 files changed, 17 insertions(+), 37 deletions(-)
> 
> Index: linux.trees.git/drivers/cpuidle/cpuidle.c
> ===================================================================
> --- linux.trees.git.orig/drivers/cpuidle/cpuidle.c
> +++ linux.trees.git/drivers/cpuidle/cpuidle.c
> @@ -24,9 +24,14 @@ DEFINE_PER_CPU(struct cpuidle_device *, 
> 
>  DEFINE_MUTEX(cpuidle_lock);
>  LIST_HEAD(cpuidle_detected_devices);
> -static void (*pm_idle_old)(void);
> 
>  static int enabled_devices;
> +static int idle_function_registered;
> +
> +struct idle_function_desc cpuidle_idle_desc = {
> +	.name           =       "cpuidle_loop",
> +	.idle_func      =       cpuidle_idle_call,
> +};
> 
>  #if defined(CONFIG_ARCH_HAS_CPU_IDLE_WAIT)
>  static void cpuidle_kick_cpus(void)
> @@ -54,13 +59,10 @@ static void cpuidle_idle_call(void)
> 
>  	/* check if the device is ready */
>  	if (!dev || !dev->enabled) {
> -		if (pm_idle_old)
> -			pm_idle_old();
> -		else
>  #if defined(CONFIG_ARCH_HAS_DEFAULT_IDLE)
> -			default_idle();
> +		default_idle();
>  #else
> -			local_irq_enable();
> +		local_irq_enable();
>  #endif
>  		return;
>  	}
> @@ -94,35 +96,11 @@ static void cpuidle_idle_call(void)
>  }
> 
>  /**
> - * cpuidle_install_idle_handler - installs the cpuidle idle loop handler
> - */
> -void cpuidle_install_idle_handler(void)
> -{
> -	if (enabled_devices && (pm_idle != cpuidle_idle_call)) {
> -		/* Make sure all changes finished before we switch to new idle */
> -		smp_wmb();
> -		pm_idle = cpuidle_idle_call;
> -	}
> -}
> -
> -/**
> - * cpuidle_uninstall_idle_handler - uninstalls the cpuidle idle loop handler
> - */
> -void cpuidle_uninstall_idle_handler(void)
> -{
> -	if (enabled_devices && pm_idle_old && (pm_idle != pm_idle_old)) {
> -		pm_idle = pm_idle_old;
> -		cpuidle_kick_cpus();
> -	}
> -}
> -
> -/**
>   * cpuidle_pause_and_lock - temporarily disables CPUIDLE
>   */
>  void cpuidle_pause_and_lock(void)
>  {
>  	mutex_lock(&cpuidle_lock);
> -	cpuidle_uninstall_idle_handler();
>  }
> 
>  EXPORT_SYMBOL_GPL(cpuidle_pause_and_lock);
> @@ -132,7 +110,6 @@ EXPORT_SYMBOL_GPL(cpuidle_pause_and_lock
>   */
>  void cpuidle_resume_and_unlock(void)
>  {
> -	cpuidle_install_idle_handler();
>  	mutex_unlock(&cpuidle_lock);
>  }
> 

What does this mean for users of cpuidle_pause_and_lock/unlock?
Should we be calling register/unregister_idle_function here?


> @@ -287,6 +264,12 @@ static int __cpuidle_register_device(str
>  	return 0;
>  }
> 
> +static void register_cpuidle_idle_function(void)
> +{
> +	register_idle_function(&cpuidle_idle_desc);
> +
> +	idle_function_registered = 1;

Use booleans if possible, unless you intend to extend the meaning of
registered someday.

> +}
>  /**
>   * cpuidle_register_device - registers a CPU's idle PM feature
>   * @dev: the cpu
> @@ -303,7 +286,9 @@ int cpuidle_register_device(struct cpuid
>  	}
> 
>  	cpuidle_enable_device(dev);
> -	cpuidle_install_idle_handler();
> +
> +	if (!idle_function_registered)
> +		register_cpuidle_idle_function();
> 
>  	mutex_unlock(&cpuidle_lock);
> 
> @@ -382,8 +367,6 @@ static int __init cpuidle_init(void)
>  {
>  	int ret;
> 
> -	pm_idle_old = pm_idle;
> -
>  	ret = cpuidle_add_class_sysfs(&cpu_sysdev_class);
>  	if (ret)
>  		return ret;
> Index: linux.trees.git/drivers/cpuidle/governor.c
> ===================================================================
> --- linux.trees.git.orig/drivers/cpuidle/governor.c
> +++ linux.trees.git/drivers/cpuidle/governor.c
> @@ -48,8 +48,6 @@ int cpuidle_switch_governor(struct cpuid
>  	if (gov == cpuidle_curr_governor)
>  		return 0;
> 
> -	cpuidle_uninstall_idle_handler();
> -
>  	if (cpuidle_curr_governor) {
>  		list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
>  			cpuidle_disable_device(dev);
> @@ -63,7 +61,6 @@ int cpuidle_switch_governor(struct cpuid
>  			return -EINVAL;
>  		list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
>  			cpuidle_enable_device(dev);
> -		cpuidle_install_idle_handler();
>  		printk(KERN_INFO "cpuidle: using governor %s\n", gov->name);
>  	}
> 

-- 
	Balbir