From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [Eas-dev] [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq callbacks Date: Thu, 27 Jul 2017 12:44:41 +0530 Message-ID: <20170727071441.GL352@vireshk-i7> References: <8797d4993baa6580e3af741d081be492032ce9dd.1501060871.git.viresh.kumar@linaro.org> <20170727055026.GK352@vireshk-i7> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pg0-f48.google.com ([74.125.83.48]:37010 "EHLO mail-pg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751595AbdG0HOp (ORCPT ); Thu, 27 Jul 2017 03:14:45 -0400 Received: by mail-pg0-f48.google.com with SMTP id y129so94278114pgy.4 for ; Thu, 27 Jul 2017 00:14:45 -0700 (PDT) Content-Disposition: inline In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Joel Fernandes (Google)" Cc: Rafael Wysocki , Srinivas Pandruvada , Len Brown , Ingo Molnar , Peter Zijlstra , linux-pm@vger.kernel.org, Linux Kernel Mailing List , smuckle.linux@gmail.com, eas-dev@lists.linaro.org, Joel Fernandes On 26-07-17, 23:13, Joel Fernandes (Google) wrote: > On Wed, Jul 26, 2017 at 10:50 PM, Viresh Kumar wrote: > > On 26-07-17, 22:34, Joel Fernandes (Google) wrote: > >> On Wed, Jul 26, 2017 at 2:22 AM, Viresh Kumar wrote: > >> > @@ -221,7 +226,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time, > >> > sugov_set_iowait_boost(sg_cpu, time, flags); > >> > sg_cpu->last_update = time; > >> > > >> > - if (!sugov_should_update_freq(sg_policy, time)) > >> > + if (!sugov_should_update_freq(sg_policy, time, hook->cpu)) > >> > return; > >> > >> Since with the remote callbacks now possible, isn't it unsafe to > >> modify sg_cpu and sg_policy structures without a lock in > >> sugov_update_single? > >> > >> Unlike sugov_update_shared, we don't acquire any lock in > >> sugov_update_single before updating these structures. Did I miss > >> something? > > > > As Peter already mentioned it earlier, the callbacks are called with > > rq locks held and so sugov_update_single() wouldn't get called in > > parallel for a target CPU. > > Ah ok, I have to catch up with that discussion since I missed the > whole thing. Now that you will have me on CC, that shouldn't happen, > thanks and sorry about the noise. > > > That's the only race you were worried about ? > > Yes. So then in that case, makes sense to move raw_spin_lock in > sugov_update_shared further down? (Just discussing, this point is > independent of your patch), Something like: Even that was discussed tomorrow with Peter :) No it wouldn't work because sg_cpu->util we are updating here may be getting read from some other cpu that shares policy with sg_cpu. -- viresh