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SubjectRe: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests
On 09-05-18, 10:30, Rafael J. Wysocki wrote:
> On Wed, May 9, 2018 at 10:06 AM, Joel Fernandes <joel@joelfernandes.org> wrote:
> > How about this? Will use the latest request, and also doesn't do unnecessary
> > irq_work_queue:

I almost wrote the same stuff before I went for lunch :)

> > (untested)
> > -----8<--------
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index d2c6083304b4..6a3e42b01f52 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -38,7 +38,7 @@ struct sugov_policy {
> > struct mutex work_lock;
> > struct kthread_worker worker;
> > struct task_struct *thread;
> > - bool work_in_progress;
> > + bool work_in_progress; /* Has kthread been kicked */
> >
> > bool need_freq_update;
> > };
> > @@ -92,9 +92,6 @@ static bool sugov_should_update_freq(struct sugov_policy *sg_policy, u64 time)
> > !cpufreq_can_do_remote_dvfs(sg_policy->policy))
> > return false;
> >
> > - if (sg_policy->work_in_progress)
> > - return false;
> > -
>
> Why this change?
>
> Doing the below is rather pointless if work_in_progress is set, isn't it?
>
> You'll drop the results of it on the floor going forward anyway then AFAICS.
>
> > if (unlikely(sg_policy->need_freq_update)) {
> > sg_policy->need_freq_update = false;
> > /*
> > @@ -129,8 +126,11 @@ static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> > policy->cur = next_freq;
> > trace_cpu_frequency(next_freq, smp_processor_id());
> > } else {
> > - sg_policy->work_in_progress = true;
> > - irq_work_queue(&sg_policy->irq_work);
> > + /* work_in_progress helps us not queue unnecessarily */
> > + if (!sg_policy->work_in_progress) {
> > + sg_policy->work_in_progress = true;
> > + irq_work_queue(&sg_policy->irq_work);
> > + }
> > }
> > }

Right, none of the above changes are required now.

> > @@ -381,13 +381,23 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
> > static void sugov_work(struct kthread_work *work)
> > {
> > struct sugov_policy *sg_policy = container_of(work, struct sugov_policy, work);
> > + unsigned int freq;
> > +
> > + /*
> > + * Hold sg_policy->update_lock just enough to handle the case where:
> > + * if sg_policy->next_freq is updated before work_in_progress is set to
> > + * false, we may miss queueing the new update request since
> > + * work_in_progress would appear to be true.
> > + */
> > + raw_spin_lock(&sg_policy->update_lock);
> > + freq = sg_policy->next_freq;
> > + sg_policy->work_in_progress = false;
> > + raw_spin_unlock(&sg_policy->update_lock);

One problem we still have is that sg_policy->update_lock is only used
in the shared policy case and not in the single CPU per policy case,
so the race isn't solved there yet.

> > mutex_lock(&sg_policy->work_lock);
> > - __cpufreq_driver_target(sg_policy->policy, sg_policy->next_freq,
> > + __cpufreq_driver_target(sg_policy->policy, freq,
> > CPUFREQ_RELATION_L);
> > mutex_unlock(&sg_policy->work_lock);
> > -
> > - sg_policy->work_in_progress = false;
> > }
> >
> > static void sugov_irq_work(struct irq_work *irq_work)

--
viresh

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