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?
Yes, I was also thinking the same. I think we can come up with a better
mechanism that still doesn't use work_in_progress. I am cooking up a patch
but may take a bit longer since I'm traveling. I'll share it once I have
something :)
thanks,
- Joel
