Messages in this thread | | | Date | Wed, 9 May 2018 01:51:16 -0700 | From | Joel Fernandes <> | Subject | Re: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests |
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On Wed, May 09, 2018 at 10:30:37AM +0200, Rafael J. Wysocki wrote: > On Wed, May 9, 2018 at 10:06 AM, Joel Fernandes <joel@joelfernandes.org> wrote: > > 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; > > - > > Why this change? > > Doing the below is rather pointless if work_in_progress is set, isn't it?
The issue being discussed is that if a work was already in progress, then new frequency updates will be dropped. So say even if DL increased in utilization, nothing will happen because if work_in_progress = true and need_freq_update = true, we would skip an update. In this diff, I am allowing the frequency request to be possible while work_in_progress is true. In the end the latest update will be picked.
> > You'll drop the results of it on the floor going forward anyway then AFAICS.
Why? If sg_policy->need_freq_update = true, sugov_should_update_freq() will return true.
thanks,
- Joel
> > > 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)
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