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SubjectRe: [PATCH V2 6/7] thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver
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On 27/03/2018 05:35, Leo Yan wrote:
> On Wed, Feb 21, 2018 at 04:29:27PM +0100, Daniel Lezcano wrote:
>
> [...]
>
>> +/**
>> + * cpuidle_cooling_injection_thread - Idle injection mainloop thread function
>> + * @arg: a void pointer containing the idle cooling device address
>> + *
>> + * This main function does basically two operations:
>> + *
>> + * - Goes idle for a specific amount of time
>> + *
>> + * - Sets a timer to wake up all the idle injection threads after a
>> + * running period
>> + *
>> + * That happens only when the mitigation is enabled, otherwise the
>> + * task is scheduled out.
>> + *
>> + * In order to keep the tasks synchronized together, it is the last
>> + * task exiting the idle period which is in charge of setting the
>> + * timer.
>> + *
>> + * This function never returns.
>> + */
>> +static int cpuidle_cooling_injection_thread(void *arg)
>> +{
>> + struct sched_param param = { .sched_priority = MAX_USER_RT_PRIO/2 };
>
> I am just wandering if should set priority to (MAX_RT_PRIO - 1)?
> Otherwise I am concern it might be cannot enter deep idle state when
> any CPU idle injection thread is preempted by other higher priority RT
> threads so all CPUs have no alignment for idle state entering/exiting.

I do believe we should consider other RT tasks more important than the
idle injection threads.

>> + struct cpuidle_cooling_device *idle_cdev = arg;
>> + struct cpuidle_cooling_tsk *cct = per_cpu_ptr(&cpuidle_cooling_tsk,
>> + smp_processor_id());
>> + DEFINE_WAIT(wait);
>> +
>> + set_freezable();
>> +
>> + sched_setscheduler(current, SCHED_FIFO, &param);
>> +
>> + while (1) {
>> + s64 next_wakeup;
>> +
>> + prepare_to_wait(&cct->waitq, &wait, TASK_INTERRUPTIBLE);
>> +
>> + schedule();
>> +
>> + atomic_inc(&idle_cdev->count);
>> +
>> + play_idle(idle_cdev->idle_cycle / USEC_PER_MSEC);
>> +
>> + /*
>> + * The last CPU waking up is in charge of setting the
>> + * timer. If the CPU is hotplugged, the timer will
>> + * move to another CPU (which may not belong to the
>> + * same cluster) but that is not a problem as the
>> + * timer will be set again by another CPU belonging to
>> + * the cluster, so this mechanism is self adaptive and
>> + * does not require any hotplugging dance.
>> + */
>> + if (!atomic_dec_and_test(&idle_cdev->count))
>> + continue;
>> +
>> + if (!idle_cdev->state)
>> + continue;
>> +
>> + next_wakeup = cpuidle_cooling_runtime(idle_cdev);
>> +
>> + hrtimer_start(&idle_cdev->timer, ns_to_ktime(next_wakeup),
>> + HRTIMER_MODE_REL_PINNED);
>
> If SoC temperature descreases under tipping point, will the timer be
> disabled for this case? Or will here set next timer event with big
> value from next_wakeup?

Another timer (the polling one) will update the 'state' variable to zero
in the set_cur_state. In the worst case, we check the idle_cdev->state
right before it is updated and we end up with an extra idle injection
cycle which is perfectly fine.





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