From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Srivatsa S. Bhat" Subject: Re: [RFC v3] cpufreq: Make sure frequency transitions are serialized Date: Thu, 20 Mar 2014 14:02:40 +0530 Message-ID: <532AA7A8.3040508@linux.vnet.ibm.com> References: <2efc621827cbd96a05a3d34075154974b4816ecd.1394782795.git.viresh.kumar@linaro.org> <532840FD.308@linux.vnet.ibm.com> <53296870.5010505@linux.vnet.ibm.com> <53298A7D.3080400@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from e23smtp09.au.ibm.com ([202.81.31.142]:42085 "EHLO e23smtp09.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751605AbaCTIdH (ORCPT ); Thu, 20 Mar 2014 04:33:07 -0400 Received: from /spool/local by e23smtp09.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 20 Mar 2014 18:33:04 +1000 In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar Cc: "Rafael J. Wysocki" , Lists linaro-kernel , "cpufreq@vger.kernel.org" , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , Amit Daniel On 03/20/2014 10:09 AM, Viresh Kumar wrote: > On 19 March 2014 17:45, Srivatsa S. Bhat > wrote: >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >> index 199b52b..e90388f 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c >> @@ -349,6 +349,38 @@ void cpufreq_notify_post_transition(struct cpufreq_policy *policy, >> EXPORT_SYMBOL_GPL(cpufreq_notify_post_transition); >> >> >> +void cpufreq_freq_transition_begin(struct cpufreq_policy *policy, >> + struct cpufreq_freqs *freqs, unsigned int state) >> +{ >> +wait: >> + wait_event(&policy->transition_wait, !policy->transition_ongoing); > > I think its broken here. At this point another thread can come take lock, > update transition_ongoing, send notification and finally unlock.. > > And after that we can take the lock and send another notification.. > > Correct? > Good catch! I missed that yesterday. Please find the updated patch below, with all your suggestions incorporated. Does this version look any better? ------------------------------------------------------------------------ diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index 199b52b..5283f10 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -349,6 +349,39 @@ void cpufreq_notify_post_transition(struct cpufreq_policy *policy, EXPORT_SYMBOL_GPL(cpufreq_notify_post_transition); +void cpufreq_freq_transition_begin(struct cpufreq_policy *policy, + struct cpufreq_freqs *freqs, unsigned int state) +{ +wait: + wait_event(&policy->transition_wait, !policy->transition_ongoing); + + mutex_lock(&policy->transition_lock); + + if (policy->transition_ongoing) { + mutex_unlock(&policy->transition_lock); + goto wait; + } + + policy->transition_ongoing = true; + + mutex_unlock(&policy->transition_lock); + + cpufreq_notify_transition(policy, freqs, CPUFREQ_PRECHANGE); +} + +void cpufreq_freq_transition_end(struct cpufreq_policy *policy, + struct cpufreq_freqs *freqs, unsigned int state) +{ + cpufreq_notify_transition(policy, freqs, CPUFREQ_POSTCHANGE); + + mutex_lock(&policy->transition_lock); + policy->transition_ongoing = false; + mutex_unlock(&policy->transition_lock); + + wake_up(&policy->transition_wait); +} + + /********************************************************************* * SYSFS INTERFACE * *********************************************************************/ @@ -968,6 +1001,8 @@ static struct cpufreq_policy *cpufreq_policy_alloc(void) INIT_LIST_HEAD(&policy->policy_list); init_rwsem(&policy->rwsem); + mutex_init(&policy->transition_lock); + init_waitqueue_head(&policy->transition_wait); return policy; diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 4d89e0e..8bded24 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -101,6 +101,11 @@ struct cpufreq_policy { * __cpufreq_governor(data, CPUFREQ_GOV_POLICY_EXIT); */ struct rw_semaphore rwsem; + + /* Synchronization for frequency transitions */ + bool transition_ongoing; /* Tracks transition status */ + struct mutex transition_lock; + wait_queue_head_t transition_wait; }; /* Only for ACPI */