Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Wed, 9 May 2018 10:30:37 +0200 | Subject | Re: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests |
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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?
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); > + } > } > } > > @@ -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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