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SubjectRe: [RFC PATCH v4 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost
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On 1/23/20 9:02 PM, Rafael J. Wysocki wrote:
> On Thu, Jan 23, 2020 at 6:21 PM Douglas Raillard
> <douglas.raillard@arm.com> wrote:
>>
>>
>>
>> On 1/23/20 3:55 PM, Rafael J. Wysocki wrote:
>>> On Wed, Jan 22, 2020 at 6:36 PM Douglas RAILLARD
>>> <douglas.raillard@arm.com> wrote:
>>>>
>>>> Use the utilization signals dynamic to detect when the utilization of a
>>>> set of tasks starts increasing because of a change in tasks' behavior.
>>>> This allows detecting when spending extra power for faster frequency
>>>> ramp up response would be beneficial to the reactivity of the system.
>>>>
>>>> This ramp boost is computed as the difference between util_avg and
>>>> util_est_enqueued. This number somehow represents a lower bound of how
>>>> much extra utilization this tasks is actually using, compared to our
>>>> best current stable knowledge of it (which is util_est_enqueued).
>>>>
>>>> When the set of runnable tasks changes, the boost is disabled as the
>>>> impact of blocked utilization on util_avg will make the delta with
>>>> util_est_enqueued not very informative.
>>>>
>>>> Signed-off-by: Douglas RAILLARD <douglas.raillard@arm.com>
>>>> ---
>>>> kernel/sched/cpufreq_schedutil.c | 43 ++++++++++++++++++++++++++++++++
>>>> 1 file changed, 43 insertions(+)
>>>>
>>>> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
>>>> index 608963da4916..25a410a1ff6a 100644
>>>> --- a/kernel/sched/cpufreq_schedutil.c
>>>> +++ b/kernel/sched/cpufreq_schedutil.c
>>>> @@ -61,6 +61,10 @@ struct sugov_cpu {
>>>> unsigned long bw_dl;
>>>> unsigned long max;
>>>>
>>>> + unsigned long ramp_boost;
>>>> + unsigned long util_est_enqueued;
>>>> + unsigned long util_avg;
>>>> +
>>>> /* The field below is for single-CPU policies only: */
>>>> #ifdef CONFIG_NO_HZ_COMMON
>>>> unsigned long saved_idle_calls;
>>>> @@ -183,6 +187,42 @@ static void sugov_deferred_update(struct sugov_policy *sg_policy, u64 time,
>>>> }
>>>> }
>>>>
>>>> +static unsigned long sugov_cpu_ramp_boost(struct sugov_cpu *sg_cpu)
>>>> +{
>>>> + return READ_ONCE(sg_cpu->ramp_boost);
>>>> +}
>>>
>>> Where exactly is this function used?
>>
>> In the next commit where the boost value is actually used to do
>> something. The function is introduced here to keep the
>> WRITE_ONCE/READ_ONCE pair together.
>
> But ramp_boost itself is not really used in this patch too AFAICS.

I'll squash that patch with the next one where it's actually used then:
sched/cpufreq: Boost schedutil frequency ramp up

Thanks,
Douglas

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