Re: [PATCH v7 06/26] timer: Export next wakeup time of a CPU

[Ulf Hansson <ulf.hansson@linaro.org>]

On 13 April 2018 at 10:47, Rafael J. Wysocki <rafael@kernel.org> wrote:
> On Thu, Apr 12, 2018 at 1:14 PM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> From: Lina Iyer <lina.iyer@linaro.org>
>>
>> Knowing the sleep duration of CPUs, is known to be needed while selecting
>> the most energy efficient idle state for a CPU or a group of CPUs.
>>
>> However, to be able to compute the sleep duration, we need to know at what
>> time the next expected wakeup is for the CPU. Therefore, let's export this
>> information via a new function, tick_nohz_get_next_wakeup(). Following
>> changes make use of it.
>>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
>> Cc: Lina Iyer <ilina@codeaurora.org>
>> Cc: Frederic Weisbecker <fweisbec@gmail.com>
>> Cc: Ingo Molnar <mingo@kernel.org>
>> Signed-off-by: Lina Iyer <lina.iyer@linaro.org>
>> Co-developed-by: Ulf Hansson <ulf.hansson@linaro.org>
>> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
>> ---
>>  include/linux/tick.h     | 10 ++++++++++
>>  kernel/time/tick-sched.c | 11 +++++++++++
>>  2 files changed, 21 insertions(+)
>>
>> diff --git a/include/linux/tick.h b/include/linux/tick.h
>> index 389aa25..d341811 100644
>> --- a/include/linux/tick.h
>> +++ b/include/linux/tick.h
>> @@ -125,6 +125,7 @@ extern bool tick_nohz_idle_got_tick(void);
>>  extern ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next);
>>  extern unsigned long tick_nohz_get_idle_calls(void);
>>  extern unsigned long tick_nohz_get_idle_calls_cpu(int cpu);
>> +extern ktime_t tick_nohz_get_next_wakeup(int cpu);
>>  extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
>>  extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
>>
>> @@ -151,6 +152,15 @@ static inline ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next)
>>         *delta_next = TICK_NSEC;
>>         return *delta_next;
>>  }
>> +
>> +static inline ktime_t tick_nohz_get_next_wakeup(int cpu)
>> +{
>> +       ktime_t t;
>> +
>> +       /* Next wake up is the tick period, assume it starts now */
>> +       return ktime_add(tick_nohz_get_sleep_length(&t), ktime_get());
>> +}
>
> Well, given that tick_nohz_get_sleep_length() is just the above in
> this case, wouldn't it be simpler to return ktime_add(ktime_get(),
> TICK_NSEC) from here?

Yes!

>
>> +
>>  static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
>>  static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
>>
>> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
>> index 646645e..08db7f3 100644
>> --- a/kernel/time/tick-sched.c
>> +++ b/kernel/time/tick-sched.c
>> @@ -1098,6 +1098,17 @@ unsigned long tick_nohz_get_idle_calls(void)
>>         return ts->idle_calls;
>>  }
>>
>> +/**
>> + * tick_nohz_get_next_wakeup - return the next wake up of the CPU
>> + */
>> +ktime_t tick_nohz_get_next_wakeup(int cpu)
>> +{
>> +       struct clock_event_device *dev =
>> +                       per_cpu(tick_cpu_device.evtdev, cpu);
>
> I would avoid breaking the line, honestly.

Alright, I have no problem with that.

[,,,]

Thanks for reviewing!

Kind regards
Uffe