Re: [PATCH V6 2/3] cpuidle: play_idle: Specify play_idle with an idle state

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

On Fri, Nov 8, 2019 at 2:33 PM Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>
> On 08/11/2019 11:56, Rafael J. Wysocki wrote:
> > On Fri, Nov 8, 2019 at 11:47 AM Daniel Lezcano
> > <daniel.lezcano@linaro.org> wrote:
> >>
> >> On 08/11/2019 02:20, Rafael J. Wysocki wrote:
> >>> On Wednesday, October 30, 2019 8:51:40 AM CET Daniel Lezcano wrote:
> >>>> Currently, the play_idle function does not allow to tell which idle
> >>>> state we want to go. Improve this by passing the idle state as
> >>>> parameter to the function.
> >>>>
> >>>> Export cpuidle_find_deepest_state() symbol as it is used from the
> >>>> intel_powerclamp driver as a module.
> >>>>
> >>>> There is no functional changes, the cpuidle state is the deepest one.
> >>>>
> >>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> >>>> Acked-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> >>>> Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
> >>>> ---
> >>>>   V6:
> >>>>    - Change variable name 'state' -> 'index':
> >>>>      https://lkml.org/lkml/2019/10/28/874
> >>>>   V4:
> >>>>    - Add EXPORT_SYMBOL_GPL(cpuidle_find_deepest_state) for the
> >>>>      intel_powerclamp driver when this one is compiled as a module
> >>>>   V3:
> >>>>    - Add missing cpuidle.h header
> >>>> ---
> >>>>  drivers/cpuidle/cpuidle.c                | 1 +
> >>>>  drivers/powercap/idle_inject.c           | 4 +++-
> >>>>  drivers/thermal/intel/intel_powerclamp.c | 4 +++-
> >>>>  include/linux/cpu.h                      | 2 +-
> >>>>  kernel/sched/idle.c                      | 4 ++--
> >>>>  5 files changed, 10 insertions(+), 5 deletions(-)
> >>>>
> >>>> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> >>>> index 18523ea6b11b..b871fc2e8e67 100644
> >>>> --- a/drivers/cpuidle/cpuidle.c
> >>>> +++ b/drivers/cpuidle/cpuidle.c
> >>>> @@ -126,6 +126,7 @@ int cpuidle_find_deepest_state(void)
> >>>>
> >>>>      return find_deepest_state(drv, dev, UINT_MAX, 0, false);
> >>>>  }
> >>>> +EXPORT_SYMBOL_GPL(cpuidle_find_deepest_state);
> >>>
> >>> That doesn't appear to be really necessary to me.
> >>>
> >>>>
> >>>>  #ifdef CONFIG_SUSPEND
> >>>>  static void enter_s2idle_proper(struct cpuidle_driver *drv,
> >>>> diff --git a/drivers/powercap/idle_inject.c b/drivers/powercap/idle_inject.c
> >>>> index cd1270614cc6..233c878cbf46 100644
> >>>> --- a/drivers/powercap/idle_inject.c
> >>>> +++ b/drivers/powercap/idle_inject.c
> >>>> @@ -38,6 +38,7 @@
> >>>>  #define pr_fmt(fmt) "ii_dev: " fmt
> >>>>
> >>>>  #include <linux/cpu.h>
> >>>> +#include <linux/cpuidle.h>
> >>>>  #include <linux/hrtimer.h>
> >>>>  #include <linux/kthread.h>
> >>>>  #include <linux/sched.h>
> >>>> @@ -138,7 +139,8 @@ static void idle_inject_fn(unsigned int cpu)
> >>>>       */
> >>>>      iit->should_run = 0;
> >>>>
> >>>> -    play_idle(READ_ONCE(ii_dev->idle_duration_us));
> >>>> +    play_idle(READ_ONCE(ii_dev->idle_duration_us),
> >>>> +              cpuidle_find_deepest_state());
> >>>
> >>> The next patch changes this again and I'm not sure why this intermediate
> >>> change is useful.
> >>>
> >>>>  }
> >>>>
> >>>>  /**
> >>>> diff --git a/drivers/thermal/intel/intel_powerclamp.c b/drivers/thermal/intel/intel_powerclamp.c
> >>>> index 53216dcbe173..b55786c169ae 100644
> >>>> --- a/drivers/thermal/intel/intel_powerclamp.c
> >>>> +++ b/drivers/thermal/intel/intel_powerclamp.c
> >>>> @@ -29,6 +29,7 @@
> >>>>  #include <linux/delay.h>
> >>>>  #include <linux/kthread.h>
> >>>>  #include <linux/cpu.h>
> >>>> +#include <linux/cpuidle.h>
> >>>>  #include <linux/thermal.h>
> >>>>  #include <linux/slab.h>
> >>>>  #include <linux/tick.h>
> >>>> @@ -430,7 +431,8 @@ static void clamp_idle_injection_func(struct kthread_work *work)
> >>>>      if (should_skip)
> >>>>              goto balance;
> >>>>
> >>>> -    play_idle(jiffies_to_usecs(w_data->duration_jiffies));
> >>>> +    play_idle(jiffies_to_usecs(w_data->duration_jiffies),
> >>>> +              cpuidle_find_deepest_state());
> >>>
> >>> I don't see a reason for changing the code here like this.
> >>>
> >>> What you really need is to have a way to set a limit on the idle
> >>> state exit latency for idle injection on ARM.
> >>
> >> Mmh, yes you are right. The idle state number is part of the internals
> >> of the cpuidle framework while the exit latency is an input (from user
> >> or kernel).
> >>
> >>> For that you can pass the exit latency limit to play_idle(), but then
> >>> you need to change powerclamp to pass UNIT_MAX or similar which is
> >>> ugly, or you can redefine cpuidle_use_deepest_state() to take the
> >>> exit latency limit as the arg (with 0 meaning use_deepest_state == false).
> >>
> >> Should it make sense to just get the resume latency in
> >> cpuidle_use_deepest_state() and pass the value to find_deepest_state()?
> >
> > Yes, I would change cpuidle_use_deepest_state() to take the max exit
> > latency as the arg (maybe with 0 meaning "don't use the deepest state
> > only any more").
>
> Why not simply ?
>
> int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
>                                 struct cpuidle_device *dev)
> {
>         int latency = cpuidle_governor_latency_req(dev->cpu);
>
>         return find_deepest_state(drv, dev, latency_req, 0, false);
> }

Because, AFAICS, that doesn't work for powerclamp.