Messages in this thread Patch in this message | | | Date | Wed, 9 May 2018 01:06:44 -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 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)
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