Re: [patch 2/5] cpuidle: add get_poll_time callback

["Rafael J. Wysocki" <rafael@kernel.org>]

On Mon, Jul 1, 2019 at 8:57 PM Marcelo Tosatti <mtosatti@redhat.com> wrote:
>
> Add a "get_poll_time" callback to the cpuidle_governor structure,
> and change poll state to poll for that amount of time.
>
> Provide a default method for it, while allowing individual governors
> to override it.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

I had ACKed this before, but then it occurred to me that it would be
less intrusive to use a new field, say poll_limit_ns (equal to 0 by
default), in struct cpuidle_device.

>
> ---
>  drivers/cpuidle/cpuidle.c    |   40 ++++++++++++++++++++++++++++++++++++++++
>  drivers/cpuidle/poll_state.c |   11 ++---------
>  include/linux/cpuidle.h      |    8 ++++++++
>  3 files changed, 50 insertions(+), 9 deletions(-)
>
> Index: linux-2.6-newcpuidle.git/drivers/cpuidle/cpuidle.c
> ===================================================================
> --- linux-2.6-newcpuidle.git.orig/drivers/cpuidle/cpuidle.c
> +++ linux-2.6-newcpuidle.git/drivers/cpuidle/cpuidle.c
> @@ -362,6 +362,46 @@ void cpuidle_reflect(struct cpuidle_devi
>  }
>
>  /**
> + * cpuidle_default_poll_time - default routine used to return poll time
> + * governors can override it if necessary
> + *
> + * @drv:   the cpuidle driver tied with the cpu
> + * @dev:   the cpuidle device
> + *
> + */
> +static u64 cpuidle_default_poll_time(struct cpuidle_driver *drv,
> +                                    struct cpuidle_device *dev)

With this new field in place this could be called cpuidle_poll_time() and ->

> +{
> +       int i;

-> do something like this here:

if (dev->poll_limit_ns)
        return dev->poll_limit_ns;

and the governor changes below wouldn't be necessary any more.

Then, the governor could update poll_limit_ns if it wanted to override
the default.

It also would be possible to use poll_limit_ns as a sort of poll limit
cache to store the last value in it and clear it on state
disable/enable to avoid the search through the states every time even
without haltpoll.

> +
> +       for (i = 1; i < drv->state_count; i++) {
> +               if (drv->states[i].disabled || dev->states_usage[i].disable)
> +                       continue;
> +
> +               return (u64)drv->states[i].target_residency * NSEC_PER_USEC;
> +       }
> +
> +       return TICK_NSEC;
> +}
> +
> +/**
> + * cpuidle_get_poll_time - tell the polling driver how much time to poll,
> + *                        in nanoseconds.
> + *
> + * @drv: the cpuidle driver tied with the cpu
> + * @dev: the cpuidle device
> + *
> + */
> +u64 cpuidle_get_poll_time(struct cpuidle_driver *drv,
> +                         struct cpuidle_device *dev)
> +{
> +       if (cpuidle_curr_governor->get_poll_time)
> +               return cpuidle_curr_governor->get_poll_time(drv, dev);
> +
> +       return cpuidle_default_poll_time(drv, dev);
> +}
> +
> +/**
>   * cpuidle_install_idle_handler - installs the cpuidle idle loop handler
>   */
>  void cpuidle_install_idle_handler(void)
> Index: linux-2.6-newcpuidle.git/drivers/cpuidle/poll_state.c
> ===================================================================
> --- linux-2.6-newcpuidle.git.orig/drivers/cpuidle/poll_state.c
> +++ linux-2.6-newcpuidle.git/drivers/cpuidle/poll_state.c
> @@ -20,16 +20,9 @@ static int __cpuidle poll_idle(struct cp
>         local_irq_enable();
>         if (!current_set_polling_and_test()) {
>                 unsigned int loop_count = 0;
> -               u64 limit = TICK_NSEC;
> -               int i;
> +               u64 limit;
>
> -               for (i = 1; i < drv->state_count; i++) {
> -                       if (drv->states[i].disabled || dev->states_usage[i].disable)
> -                               continue;
> -
> -                       limit = (u64)drv->states[i].target_residency * NSEC_PER_USEC;
> -                       break;
> -               }
> +               limit = cpuidle_get_poll_time(drv, dev);
>
>                 while (!need_resched()) {
>                         cpu_relax();
> Index: linux-2.6-newcpuidle.git/include/linux/cpuidle.h
> ===================================================================
> --- linux-2.6-newcpuidle.git.orig/include/linux/cpuidle.h
> +++ linux-2.6-newcpuidle.git/include/linux/cpuidle.h
> @@ -132,6 +132,8 @@ extern int cpuidle_select(struct cpuidle
>  extern int cpuidle_enter(struct cpuidle_driver *drv,
>                          struct cpuidle_device *dev, int index);
>  extern void cpuidle_reflect(struct cpuidle_device *dev, int index);
> +extern u64 cpuidle_get_poll_time(struct cpuidle_driver *drv,
> +                                struct cpuidle_device *dev);
>
>  extern int cpuidle_register_driver(struct cpuidle_driver *drv);
>  extern struct cpuidle_driver *cpuidle_get_driver(void);
> @@ -166,6 +168,9 @@ static inline int cpuidle_enter(struct c
>                                 struct cpuidle_device *dev, int index)
>  {return -ENODEV; }
>  static inline void cpuidle_reflect(struct cpuidle_device *dev, int index) { }
> +extern u64 cpuidle_get_poll_time(struct cpuidle_driver *drv,
> +                                struct cpuidle_device *dev)
> +{return 0; }
>  static inline int cpuidle_register_driver(struct cpuidle_driver *drv)
>  {return -ENODEV; }
>  static inline struct cpuidle_driver *cpuidle_get_driver(void) {return NULL; }
> @@ -246,6 +251,9 @@ struct cpuidle_governor {
>                                         struct cpuidle_device *dev,
>                                         bool *stop_tick);
>         void (*reflect)         (struct cpuidle_device *dev, int index);
> +
> +       u64 (*get_poll_time)    (struct cpuidle_driver *drv,
> +                                struct cpuidle_device *dev);
>  };
>
>  #ifdef CONFIG_CPU_IDLE
>
>