Messages in this thread Patch in this message | | | Date | Thu, 17 May 2018 06:07:04 -0700 | From | Joel Fernandes <> | Subject | Re: [PATCH RFC] schedutil: Allow cpufreq requests to be made even when kthread kicked |
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On Thu, May 17, 2018 at 12:53:58PM +0200, Juri Lelli wrote: > On 17/05/18 15:50, Viresh Kumar wrote: > > On 17-05-18, 09:00, Juri Lelli wrote: > > > Hi Joel, > > > > > > On 16/05/18 15:45, Joel Fernandes (Google) wrote: > > > > > > [...] > > > > > > > @@ -382,13 +391,24 @@ 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; > > > > + unsigned long flags; > > > > + > > > > + /* > > > > + * Hold sg_policy->update_lock shortly to handle the case where: > > > > + * incase sg_policy->next_freq is read here, and then updated by > > > > + * sugov_update_shared just before work_in_progress is set to false > > > > + * here, we may miss queueing the new update. > > > > + */ > > > > + raw_spin_lock_irqsave(&sg_policy->update_lock, flags); > > > > + freq = sg_policy->next_freq; > > > > + sg_policy->work_in_progress = false; > > > > + raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags); > > > > > > OK, we queue the new request up, but still we need to let this kthread > > > activation complete and then wake it up again to service the request > > > already queued, right? Wasn't what Claudio proposed (service back to > > > back requests all in the same kthread activation) better from an > > > overhead pow?
Hmm, from that perspective, yeah. But note that my patch doesn't increase the overhead from what it already is.. because we don't queue the irq_work again unless work_in_progress is cleared, which wouldn't be if the kthread didn't run yet.
> > > > We would need more locking stuff in the work handler in that case and > > I think there maybe a chance of missing the request in that solution > > if the request happens right at the end of when sugov_work returns. > > Mmm, true. Ideally we might want to use some sort of queue where to > atomically insert requests and then consume until queue is empty from > sugov kthread.
IMO we don't really need a queue or anything, we should need the kthread to process the *latest* request it sees since that's the only one that matters.
> But, I guess that's going to be too much complexity for an (hopefully) > corner case.
I thought of this corner case too, I'd argue its still an improvement over not doing anything, but we could tighten this up a bit more if you wanted by doing something like this on top of my patch. Thoughts?
---8<-----------------------
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index a87fc281893d..e45ec24b810b 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -394,6 +394,7 @@ static void sugov_work(struct kthread_work *work) unsigned int freq; unsigned long flags; +redo_work: /* * Hold sg_policy->update_lock shortly to handle the case where: * incase sg_policy->next_freq is read here, and then updated by @@ -409,6 +410,9 @@ static void sugov_work(struct kthread_work *work) __cpufreq_driver_target(sg_policy->policy, freq, CPUFREQ_RELATION_L); mutex_unlock(&sg_policy->work_lock); + + if (sg_policy->work_in_progress) + goto redo_work; } static void sugov_irq_work(struct irq_work *irq_work)
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