On Wed, May 09, 2018 at 11:06:24AM +0200, Rafael J. Wysocki wrote: > On Wed, May 9, 2018 at 10:51 AM, Joel Fernandes <[email protected]> > wrote: > > 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 <[email protected]> > >> 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. > > I'm not sure if taking new requests with the irq_work in flight is a good > idea.
That's the point of the original $SUBJECT patch posted by Claudio :) In that you can see if urgent_request, then work_in_progress isn't checked. Also I don't see why we cannot do this with this small tweak as in my diff. It solves a real problem seen with frequency updates done with the slow-switch as we discussed at OSPM. But let me know if I missed your point or something ;) > > >> > >> You'll drop the results of it on the floor going forward anyway then > >> AFAICS. > > > > Why? > > Because you cannot queue up a new irq_work before the previous one is > complete? We are not doing that. If you see in my diff, I am not queuing an irq_work if one was already queued. What we're allowing is an update to next_freq. We still use work_in_progress but don't use it to ban all incoming update requests as done previously. Instead we use work_in_progress to make sure that we dont unnecessarily increase the irq pressure and have excessive wake ups (as Juri suggested). I can clean it up and post it as a patch next week after some testing incase that's less confusing. This week I'm actually on vacation and the diff was pure vacation hacking ;-) thanks, - Joel
