From mboxrd@z Thu Jan 1 00:00:00 1970 From: Viresh Kumar Subject: Re: [PATCH][experimantal] cpufreq: governor: Use an atomic variable for synchronization Date: Tue, 8 Dec 2015 22:04:02 +0530 Message-ID: <20151208163402.GL3692@ubuntu> References: <1843141.WbisoTkq1u@vostro.rjw.lan> <20151208145658.GG3692@ubuntu> <5332935.yle75kNJGs@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pa0-f43.google.com ([209.85.220.43]:36474 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965221AbbLHQeH (ORCPT ); Tue, 8 Dec 2015 11:34:07 -0500 Received: by pacdm15 with SMTP id dm15so14386669pac.3 for ; Tue, 08 Dec 2015 08:34:06 -0800 (PST) Content-Disposition: inline In-Reply-To: <5332935.yle75kNJGs@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: linux-pm@vger.kernel.org, linaro-kernel@lists.linaro.org, ashwin.chaugule@linaro.org, "Rafael J. Wysocki" , LKML On 08-12-15, 17:42, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > Subject: [PATCH] cpufreq: governor: Use lockless timer function > > It is possible to get rid of the timer_lock spinlock used by the > governor timer function for synchronization, but a couple of races > need to be avoided. > > The first race is between multiple dbs_timer_handler() instances > that may be running in parallel with each other on different > CPUs. Namely, one of them has to queue up the work item, but it > cannot be queued up more than once. To achieve that, > atomic_inc_return() can be used on the skip_work field of > struct cpu_common_dbs_info. > > The second race is between an already running dbs_timer_handler() > and gov_cancel_work(). In that case the dbs_timer_handler() might > not notice the skip_work incrementation in gov_cancel_work() and > it might queue up its work item after gov_cancel_work() had > returned (and that work item would corrupt skip_work going > forward). To prevent that from happening, gov_cancel_work() > can be made wait for the timer function to complete (on all CPUs) > right after skip_work has been incremented. > > Signed-off-by: Rafael J. Wysocki > --- > drivers/cpufreq/cpufreq_governor.c | 49 ++++++++++++++++--------------------- > drivers/cpufreq/cpufreq_governor.h | 9 +----- > 2 files changed, 24 insertions(+), 34 deletions(-) Acked-by: Viresh Kumar -- viresh