From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934570AbeEIKei (ORCPT ); Wed, 9 May 2018 06:34:38 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:46521 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933864AbeEIKeg (ORCPT ); Wed, 9 May 2018 06:34:36 -0400 X-Google-Smtp-Source: AB8JxZqHgC444c7fmUsMqlaL3tVRZKHwVv37YAaZlDcdKYCQZE/AzRbBIHFV77OZer5vqAkkIF3FmQ== Date: Wed, 9 May 2018 03:34:34 -0700 From: Joel Fernandes To: Viresh Kumar Cc: "Rafael J. Wysocki" , Juri Lelli , Claudio Scordino , Linux Kernel Mailing List , "Rafael J . Wysocki" , Peter Zijlstra , Ingo Molnar , Patrick Bellasi , Luca Abeni , Joel Fernandes , Linux PM Subject: Re: [RFC PATCH] sched/cpufreq/schedutil: handling urgent frequency requests Message-ID: <20180509103434.GF76874@joelaf.mtv.corp.google.com> References: <1525704215-8683-1-git-send-email-claudio@evidence.eu.com> <20180508065435.bcht6dyb3rpp6gk5@vireshk-i7> <20180509045425.GA158882@joelaf.mtv.corp.google.com> <20180509064530.GA1681@localhost.localdomain> <20180509080644.GA76874@joelaf.mtv.corp.google.com> <20180509084001.bghnwpv3a3xnuxce@vireshk-i7> <20180509090259.GD76874@joelaf.mtv.corp.google.com> <20180509092823.sfph4gomnblb7jgr@vireshk-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180509092823.sfph4gomnblb7jgr@vireshk-i7> 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 Wed, May 09, 2018 at 02:58:23PM +0530, Viresh Kumar wrote: > On 09-05-18, 02:02, Joel Fernandes wrote: > > On Wed, May 09, 2018 at 02:10:01PM +0530, Viresh Kumar wrote: > > > Right, none of the above changes are required now. > > > > I didn't follow what you mean the changes are not required? I was developing > > against Linus mainline. Also I replied to Rafael's comment in the other > > thread. > > At least for the shared policy case the entire sequence of > sugov_should_update_freq() followed by sugov_update_commit() is > executed from within spinlock protected region and you are using the > same lock below. And so either the above two routines or the kthread > routine below will execute at a given point of time. > > So in case kthread has started doing the update and acquired the lock, > the util update handler will wait until the time work_in_progress is > set to false, that's not a problem we are trying to solve here. > > And if kthread hasn't acquired the lock yet and util handler has > started executing sugov_should_update_freq() .... > > And ^^^ this is where I understood that your earlier change is > actually required, so that we accumulate the latest updated next_freq > value. > > And with all that we wouldn't require a while loop in the kthread > code. Oh yeah, totally. So I think we are on the same page now about that. > > > > > @@ -381,13 +381,23 @@ 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; > > > > > + > > > > > + /* > > > > > + * Hold sg_policy->update_lock just enough to handle the case where: > > > > > + * if sg_policy->next_freq is updated before work_in_progress is set to > > > > > + * false, we may miss queueing the new update request since > > > > > + * work_in_progress would appear to be true. > > > > > + */ > > > > > + raw_spin_lock(&sg_policy->update_lock); > > > > > + freq = sg_policy->next_freq; > > > > > + sg_policy->work_in_progress = false; > > > > > + raw_spin_unlock(&sg_policy->update_lock); > > > > > > One problem we still have is that sg_policy->update_lock is only used > > > in the shared policy case and not in the single CPU per policy case, > > > so the race isn't solved there yet. > > > > True.. I can make the single CPU case acquire the update_lock very briefly > > around sugov_update_commit call in sugov_update_single. > > Rafael was very clear from the beginning that he wouldn't allow a spin > lock in the un-shared policy case :) That's fair. Probably we can just not do this trickery at all for the single case for now, incase work_in_progress is set. That way we still get the benefit for the shared case, and the single case isn't changed from what it is today. thanks, - Joel