From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juri Lelli Subject: Re: [PATCH RFC] schedutil: Allow cpufreq requests to be made even when kthread kicked Date: Thu, 17 May 2018 12:53:58 +0200 Message-ID: <20180517105358.GB22493@localhost.localdomain> References: <20180516224518.109891-1-joel@joelfernandes.org> <20180517070026.GA22493@localhost.localdomain> <20180517102024.s3dxo4uepujh5f65@vireshk-i7> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180517102024.s3dxo4uepujh5f65@vireshk-i7> Sender: linux-kernel-owner@vger.kernel.org To: Viresh Kumar Cc: "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , Peter Zijlstra , Ingo Molnar , Patrick Bellasi , Luca Abeni , Joel Fernandes , linux-pm@vger.kernel.org List-Id: linux-pm@vger.kernel.org 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? > > 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. But, I guess that's going to be too much complexity for an (hopefully) corner case.