Re: [PATCH] cpuidle : use percpu cpuidle in the core code

["Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>]

On 03/30/2012 04:18 PM, Daniel Lezcano wrote:

> The usual cpuidle initialization routines are to register the
> driver, then register a cpuidle device per cpu.
> 
> With the device's state count default initialization with the
> driver's state count, the code initialization remains mostly the
> same in the different drivers.
> 
> We can then add a new function 'cpuidle_register' where we register
> the driver and the devices. These devices can be defined in a global
> static variable in cpuidle.c. We will be able to factor out and
> remove a lot of duplicate lines of code.
> 
> As we still have some drivers, with different initialization routines,
> we keep 'cpuidle_register_driver' and 'cpuidle_register_device' as low
> level initialization routines to do some specific operations on the
> cpuidle devices.
> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> ---
>  drivers/cpuidle/cpuidle.c |   34 ++++++++++++++++++++++++++++++++++
>  include/linux/cpuidle.h   |    3 +++
>  2 files changed, 37 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index b8a1faf..2a174e8 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -23,6 +23,7 @@
>  #include "cpuidle.h"
> 
>  DEFINE_PER_CPU(struct cpuidle_device *, cpuidle_devices);
> +DEFINE_PER_CPU(struct cpuidle_device, cpuidle_device);
> 
>  DEFINE_MUTEX(cpuidle_lock);
>  LIST_HEAD(cpuidle_detected_devices);
> @@ -391,6 +392,39 @@ int cpuidle_register_device(struct cpuidle_device *dev)
> 
>  EXPORT_SYMBOL_GPL(cpuidle_register_device);
> 
> +int cpuidle_register(struct cpuidle_driver *drv)
> +{
> +	int ret, cpu;
> +	struct cpuidle_device *dev;
> +
> +	ret = cpuidle_register_driver(drv);
> +	if (ret)
> +		return ret;
> +
> +	for_each_online_cpu(cpu) {
> +		dev = &per_cpu(cpuidle_device, cpu);
> +		dev->cpu = cpu;
> +
> +		ret = cpuidle_register_device(dev);
> +		if (ret)
> +			goto out_unregister;
> +	}
> +


Isn't this racy with respect to CPU hotplug?

> +out:
> +	return ret;
> +
> +out_unregister:
> +	for_each_online_cpu(cpu) {
> +		dev = &per_cpu(cpuidle_device, cpu);
> +		cpuidle_unregister_device(dev);
> +	}
> +


This could be improved I guess.. What if the registration fails
for the first cpu itself? Then looping over entire online cpumask
would be a waste of time..

Here is a discussion on some very similar code:
https://lkml.org/lkml/2012/3/22/72
https://lkml.org/lkml/2012/3/22/143

> +	cpuidle_unregister_driver(drv);
> +
> +	goto out;
> +}
> +EXPORT_SYMBOL_GPL(cpuidle_register);
> +
>  /**
>   * cpuidle_unregister_device - unregisters a CPU's idle PM feature
>   * @dev: the cpu
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index f3ebbba..17e3d33 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -133,6 +133,7 @@ struct cpuidle_driver {
>  #ifdef CONFIG_CPU_IDLE
>  extern void disable_cpuidle(void);
>  extern int cpuidle_idle_call(void);
> +extern int cpuidle_register(struct cpuidle_driver *drv);
>  extern int cpuidle_register_driver(struct cpuidle_driver *drv);
>  struct cpuidle_driver *cpuidle_get_driver(void);
>  extern void cpuidle_unregister_driver(struct cpuidle_driver *drv);
> @@ -150,6 +151,8 @@ extern int cpuidle_wrap_enter(struct cpuidle_device *dev,
>  #else
>  static inline void disable_cpuidle(void) { }
>  static inline int cpuidle_idle_call(void) { return -ENODEV; }
> +static inline int cpuidle_register(struct cpuidle_driver *drv)
> +{return -ENODEV; }
>  static inline int cpuidle_register_driver(struct cpuidle_driver *drv)
>  {return -ENODEV; }
>  static inline struct cpuidle_driver *cpuidle_get_driver(void) {return NULL; }



Regards,
Srivatsa S. Bhat