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

From: Arun R Bharadwaj <[email-masked]>
Date: Wed, 2 Sep 2009 10:51:38 +0530

* Balbir Singh <[email-masked]> [2009-09-01 22:58:25]:

> * Arun R B <[email-masked]> [2009-09-01 17:08:40]:
> 
> > * Arun R Bharadwaj <[email-masked]> [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.
> 

Hi Balbir,

Yes, your understanding is correct. Currently, x86 exports pm_idle and
this pm_idle is set to cpuidle_idle_call inside cpuidle.c

So instead of that x86 should just export a function called
set_arch_idle() which will be called from within
register_idle_function() and set pm_idle to the idle handler which is
currently being registered.

I have implemented this for pseries, and in the process of doing it
for x86 too.

> > Also remove unwanted functions cpuidle_[un]install_idle_handler,
> > cpuidle_kick_cpus()
> >
> > Signed-off-by: Arun R Bharadwaj <[email-masked]>
> > ---
> >  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?
>

Yes, you are right. I have missed out on this part.
register/unregister_idle_function should replace
install/uninstall_idle_handler at those places. Thanks.

> 
> > @@ -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.
>

I don't intend to extend the meaning of idle_function_registered.
Will use boolean here.

> > +}
> >  /**
> >   * 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

Thanks for the review!
--arun