From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752271AbeEQO23 (ORCPT ); Thu, 17 May 2018 10:28:29 -0400 Received: from mail-wr0-f194.google.com ([209.85.128.194]:46962 "EHLO mail-wr0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751798AbeEQO21 (ORCPT ); Thu, 17 May 2018 10:28:27 -0400 X-Google-Smtp-Source: AB8JxZoaophDg+uSCGQV+o7vMTmgJu0QDsqawrIugj8pjgSbdJPzquF1D//7Qb/deIcPIKKuxQG97g== Date: Thu, 17 May 2018 16:28:23 +0200 From: Juri Lelli To: Joel Fernandes Cc: Viresh Kumar , linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , Peter Zijlstra , Ingo Molnar , Patrick Bellasi , Luca Abeni , Joel Fernandes , linux-pm@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH RFC] schedutil: Allow cpufreq requests to be made even when kthread kicked Message-ID: <20180517142823.GD22493@localhost.localdomain> References: <20180516224518.109891-1-joel@joelfernandes.org> <20180517070026.GA22493@localhost.localdomain> <20180517102024.s3dxo4uepujh5f65@vireshk-i7> <20180517105358.GB22493@localhost.localdomain> <20180517130704.GA139147@joelaf.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180517130704.GA139147@joelaf.mtv.corp.google.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/05/18 06:07, Joel Fernandes wrote: > 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. Yep, makes sense. > > 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 Indeed! :) > 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; Didn't we already queue up another irq_work at this point?