On Wed, May 09, 2018 at 08:45:30AM +0200, Juri Lelli wrote:
> On 08/05/18 21:54, Joel Fernandes wrote:
>
> [...]
>
> > Just for discussion sake, is there any need for work_in_progress? If we can
> > queue multiple work say kthread_queue_work can handle it, then just queuing
> > works whenever they are available should be Ok and the kthread loop can
> > handle them. __cpufreq_driver_target is also protected by the work lock if
> > there is any concern that can have races... only thing is rate-limiting of
> > the requests, but we are doing a rate limiting, just not for the "DL
> > increased utilization" type requests (which I don't think we are doing at
> > the
> > moment for urgent DL requests anyway).
> >
> > Following is an untested diff to show the idea. What do you think?
> >
> > thanks,
> >
> > - Joel
> >
> > ----8<---
> > diff --git a/kernel/sched/cpufreq_schedutil.c
> > b/kernel/sched/cpufreq_schedutil.c
> > index d2c6083304b4..862634ff4bf3 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -38,7 +38,6 @@ struct sugov_policy {
> > struct mutex work_lock;
> > struct kthread_worker worker;
> > struct task_struct *thread;
> > - bool work_in_progress;
> >
> > bool need_freq_update;
> > };
> > @@ -92,16 +91,8 @@ 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;
> > -
> > if (unlikely(sg_policy->need_freq_update)) {
> > sg_policy->need_freq_update = false;
> > - /*
> > - * This happens when limits change, so forget the previous
> > - * next_freq value and force an update.
> > - */
> > - sg_policy->next_freq = UINT_MAX;
> > return true;
> > }
> >
> > @@ -129,7 +120,6 @@ 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);
>
> Isn't this potentially introducing unneeded irq pressure (and doing the
> whole wakeup the kthread thing), while the already active kthread could
> simply handle multiple back-to-back requests before going to sleep?
How about this? Will use the latest request, and also doesn't do unnecessary
irq_work_queue:
(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;
-
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);
+ }
}
}
@@ -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);
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)
