Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751604AbdG0GNP (ORCPT ); Thu, 27 Jul 2017 02:13:15 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:33210 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751042AbdG0GNN (ORCPT ); Thu, 27 Jul 2017 02:13:13 -0400 MIME-Version: 1.0 In-Reply-To: <20170727055026.GK352@vireshk-i7> References: <8797d4993baa6580e3af741d081be492032ce9dd.1501060871.git.viresh.kumar@linaro.org> <20170727055026.GK352@vireshk-i7> From: "Joel Fernandes (Google)" Date: Wed, 26 Jul 2017 23:13:11 -0700 Message-ID: Subject: Re: [Eas-dev] [PATCH V4 1/3] sched: cpufreq: Allow remote cpufreq callbacks To: Viresh Kumar 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2339 Lines: 63 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: diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 622eed1b7658..9a6c12fb2c16 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -295,8 +295,6 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time, sugov_get_util(&util, &max); - raw_spin_lock(&sg_policy->update_lock); - sg_cpu->util = util; sg_cpu->max = max; sg_cpu->flags = flags; @@ -304,6 +302,8 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time, sugov_set_iowait_boost(sg_cpu, time, flags); sg_cpu->last_update = time; + raw_spin_lock(&sg_policy->update_lock); + if (sugov_should_update_freq(sg_policy, time)) { if (flags & SCHED_CPUFREQ_RT_DL) next_f = sg_policy->policy->cpuinfo.max_freq; thanks, -Joel