Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756102AbZFYWRU (ORCPT ); Thu, 25 Jun 2009 18:17:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756384AbZFYWQ4 (ORCPT ); Thu, 25 Jun 2009 18:16:56 -0400 Received: from cantor2.suse.de ([195.135.220.15]:57453 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754847AbZFYWQw (ORCPT ); Thu, 25 Jun 2009 18:16:52 -0400 From: Thomas Renninger To: Mathieu Desnoyers Subject: Re: [PATCH 1/2] CPUFREQ: Remove unneeded dbs_mutexes from ondemand and conservative governors Date: Fri, 26 Jun 2009 00:17:09 +0200 User-Agent: KMail/1.9.10 Cc: kernel@stable.org, cpufreq@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@elte.hu, rjw@sisk.pl, hidave.darkstar@gmail.com, penberg@cs.helsinki.fi, kernel-testers@vger.kernel.org, davej@redhat.com, Venkatesh Pallipadi References: <20090623193215.GA31374@elte.hu> <1245938485-12663-2-git-send-email-trenn@suse.de> <20090625142552.GA18000@Krystal> In-Reply-To: <20090625142552.GA18000@Krystal> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200906260017.10730.trenn@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 12978 Lines: 392 On Thursday 25 June 2009 04:25:52 pm Mathieu Desnoyers wrote: > * Thomas Renninger (trenn@suse.de) wrote: > > Comment from Venkatesh: > > ... > > This mutex is just serializing the changes to those variables. I could't > > think of any functionality issues of not having the lock as such. > > > > -> rip it out. > > > > CC: Venkatesh Pallipadi > > Signed-off-by: Thomas Renninger > > --- > > drivers/cpufreq/cpufreq_conservative.c | 61 > > +++----------------------------- drivers/cpufreq/cpufreq_ondemand.c | > > 48 +++---------------------- 2 files changed, 10 insertions(+), 99 > > deletions(-) > > > > diff --git a/drivers/cpufreq/cpufreq_conservative.c > > b/drivers/cpufreq/cpufreq_conservative.c index 7a74d17..6303379 100644 > > --- a/drivers/cpufreq/cpufreq_conservative.c > > +++ b/drivers/cpufreq/cpufreq_conservative.c > > @@ -18,7 +18,6 @@ > > #include > > #include > > #include > > -#include > > #include > > #include > > #include > > @@ -84,19 +83,6 @@ static DEFINE_PER_CPU(struct cpu_dbs_info_s, > > cpu_dbs_info); > > > > static unsigned int dbs_enable; /* number of CPUs using this policy */ > > > > -/* > > - * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug > > - * lock and dbs_mutex. cpu_hotplug lock should always be held before > > - * dbs_mutex. If any function that can potentially take cpu_hotplug lock > > - * (like __cpufreq_driver_target()) is being called with dbs_mutex > > taken, then - * cpu_hotplug lock should be taken before that. Note that > > cpu_hotplug lock - * is recursive for the same process. -Venki > > - * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, > > because it - * would deadlock with cancel_delayed_work_sync(), which is > > needed for proper - * raceless workqueue teardown. > > - */ > > -static DEFINE_MUTEX(dbs_mutex); > > - > > static struct workqueue_struct *kconservative_wq; > > > > static struct dbs_tuners { > > @@ -236,10 +222,7 @@ static ssize_t store_sampling_down_factor(struct > > cpufreq_policy *unused, if (ret != 1 || input > MAX_SAMPLING_DOWN_FACTOR > > || input < 1) return -EINVAL; > > > > - mutex_lock(&dbs_mutex); > > dbs_tuners_ins.sampling_down_factor = input; > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -253,10 +236,7 @@ static ssize_t store_sampling_rate(struct > > cpufreq_policy *unused, if (ret != 1) > > return -EINVAL; > > > > - mutex_lock(&dbs_mutex); > > dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate()); > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -267,16 +247,11 @@ static ssize_t store_up_threshold(struct > > cpufreq_policy *unused, int ret; > > ret = sscanf(buf, "%u", &input); > > > > - mutex_lock(&dbs_mutex); > > if (ret != 1 || input > 100 || > > - input <= dbs_tuners_ins.down_threshold) { > > - mutex_unlock(&dbs_mutex); > > + input <= dbs_tuners_ins.down_threshold) > > return -EINVAL; > > - } > > > > dbs_tuners_ins.up_threshold = input; > > - mutex_unlock(&dbs_mutex); > > Here, for instance, there might be a problem if down_threshold is > changed concurrently with a store_up_threshold() call. See that there is > a test before the modification, and we need the mutex there for it to be > consistent. Thanks, I was rather quick with the conservative changes..., but it should still be ok. It should be assured that if userspace is doing: echo x > down_threshold echo y > up_threshold that the first one will be served/finished first? If userspace is writing different values for each core to the global conservative/ondemand tunables, or you have concurent userspace tools trying to configure ondemand/conservative, it's a userspace bug. It's confusing that ondemand/conservative allows per core reads/writes to global variables and I hope to be able to provide something to change that in some days, maybe weeks. If you still can think of a possible issue, a userspace scenario would help. > > - > > return count; > > } > > > > @@ -287,17 +262,12 @@ static ssize_t store_down_threshold(struct > > cpufreq_policy *unused, int ret; > > ret = sscanf(buf, "%u", &input); > > > > - mutex_lock(&dbs_mutex); > > /* cannot be lower than 11 otherwise freq will not fall */ > > if (ret != 1 || input < 11 || input > 100 || > > - input >= dbs_tuners_ins.up_threshold) { > > - mutex_unlock(&dbs_mutex); > > + input >= dbs_tuners_ins.up_threshold) > > return -EINVAL; > > - } > > > > dbs_tuners_ins.down_threshold = input; > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -316,11 +286,9 @@ static ssize_t store_ignore_nice_load(struct > > cpufreq_policy *policy, if (input > 1) > > input = 1; > > > > - mutex_lock(&dbs_mutex); > > - if (input == dbs_tuners_ins.ignore_nice) { /* nothing to do */ > > - mutex_unlock(&dbs_mutex); > > + if (input == dbs_tuners_ins.ignore_nice) /* nothing to do */ > > return count; > > - } > > + > > dbs_tuners_ins.ignore_nice = input; > > > > /* we need to re-evaluate prev_cpu_idle */ > > @@ -332,8 +300,6 @@ static ssize_t store_ignore_nice_load(struct > > cpufreq_policy *policy, if (dbs_tuners_ins.ignore_nice) > > dbs_info->prev_cpu_nice = kstat_cpu(j).cpustat.nice; > > } > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -352,10 +318,7 @@ static ssize_t store_freq_step(struct cpufreq_policy > > *policy, > > > > /* no need to test here if freq_step is zero as the user might actually > > * want this, they would be crazy though :) */ > > - mutex_lock(&dbs_mutex); > > dbs_tuners_ins.freq_step = input; > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -566,13 +529,9 @@ static int cpufreq_governor_dbs(struct > > cpufreq_policy *policy, > > Hrm, this is where we want the mutexes removed, but I fear this is > creating a race between sysfs_create_group (sysfs file creation) and > policy initialization... This can be solved by moving this_dbs_info->enable incremenation after sysfs_create_group. But yes, I forgot that in my patch, thanks! > I'm not convinced this mutex is not needed. I am. Maybe it still takes some more thinking or step by step rework. Finding an unintrusive, riskless short term solution for .30 is a challenge, though. Thomas > Mathieu > > > if (this_dbs_info->enable) /* Already enabled */ > > break; > > > > - mutex_lock(&dbs_mutex); > > - > > rc = sysfs_create_group(&policy->kobj, &dbs_attr_group); > > - if (rc) { > > - mutex_unlock(&dbs_mutex); > > + if (rc) > > return rc; > > - } > > > > for_each_cpu(j, policy->cpus) { > > struct cpu_dbs_info_s *j_dbs_info; > > @@ -612,13 +571,9 @@ static int cpufreq_governor_dbs(struct > > cpufreq_policy *policy, CPUFREQ_TRANSITION_NOTIFIER); > > } > > dbs_timer_init(this_dbs_info); > > - > > - mutex_unlock(&dbs_mutex); > > - > > break; > > > > case CPUFREQ_GOV_STOP: > > - mutex_lock(&dbs_mutex); > > dbs_timer_exit(this_dbs_info); > > sysfs_remove_group(&policy->kobj, &dbs_attr_group); > > dbs_enable--; > > @@ -631,13 +586,9 @@ static int cpufreq_governor_dbs(struct > > cpufreq_policy *policy, cpufreq_unregister_notifier( > > &dbs_cpufreq_notifier_block, > > CPUFREQ_TRANSITION_NOTIFIER); > > - > > - mutex_unlock(&dbs_mutex); > > - > > break; > > > > case CPUFREQ_GOV_LIMITS: > > - mutex_lock(&dbs_mutex); > > if (policy->max < this_dbs_info->cur_policy->cur) > > __cpufreq_driver_target( > > this_dbs_info->cur_policy, > > @@ -646,8 +597,6 @@ static int cpufreq_governor_dbs(struct cpufreq_policy > > *policy, __cpufreq_driver_target( > > this_dbs_info->cur_policy, > > policy->min, CPUFREQ_RELATION_L); > > - mutex_unlock(&dbs_mutex); > > - > > break; > > } > > return 0; > > diff --git a/drivers/cpufreq/cpufreq_ondemand.c > > b/drivers/cpufreq/cpufreq_ondemand.c index e741c33..d080a48 100644 > > --- a/drivers/cpufreq/cpufreq_ondemand.c > > +++ b/drivers/cpufreq/cpufreq_ondemand.c > > @@ -17,7 +17,6 @@ > > #include > > #include > > #include > > -#include > > #include > > #include > > #include > > @@ -91,19 +90,6 @@ static DEFINE_PER_CPU(struct cpu_dbs_info_s, > > cpu_dbs_info); > > > > static unsigned int dbs_enable; /* number of CPUs using this policy */ > > > > -/* > > - * DEADLOCK ALERT! There is a ordering requirement between cpu_hotplug > > - * lock and dbs_mutex. cpu_hotplug lock should always be held before > > - * dbs_mutex. If any function that can potentially take cpu_hotplug lock > > - * (like __cpufreq_driver_target()) is being called with dbs_mutex > > taken, then - * cpu_hotplug lock should be taken before that. Note that > > cpu_hotplug lock - * is recursive for the same process. -Venki > > - * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, > > because it - * would deadlock with cancel_delayed_work_sync(), which is > > needed for proper - * raceless workqueue teardown. > > - */ > > -static DEFINE_MUTEX(dbs_mutex); > > - > > static struct workqueue_struct *kondemand_wq; > > > > static struct dbs_tuners { > > @@ -269,14 +255,10 @@ static ssize_t store_sampling_rate(struct > > cpufreq_policy *unused, int ret; > > ret = sscanf(buf, "%u", &input); > > > > - mutex_lock(&dbs_mutex); > > - if (ret != 1) { > > - mutex_unlock(&dbs_mutex); > > + if (ret != 1) > > return -EINVAL; > > - } > > - dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate()); > > - mutex_unlock(&dbs_mutex); > > > > + dbs_tuners_ins.sampling_rate = max(input, minimum_sampling_rate()); > > return count; > > } > > > > @@ -287,16 +269,11 @@ static ssize_t store_up_threshold(struct > > cpufreq_policy *unused, int ret; > > ret = sscanf(buf, "%u", &input); > > > > - mutex_lock(&dbs_mutex); > > if (ret != 1 || input > MAX_FREQUENCY_UP_THRESHOLD || > > - input < MIN_FREQUENCY_UP_THRESHOLD) { > > - mutex_unlock(&dbs_mutex); > > + input < MIN_FREQUENCY_UP_THRESHOLD) > > return -EINVAL; > > - } > > > > dbs_tuners_ins.up_threshold = input; > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -315,11 +292,9 @@ static ssize_t store_ignore_nice_load(struct > > cpufreq_policy *policy, if (input > 1) > > input = 1; > > > > - mutex_lock(&dbs_mutex); > > - if (input == dbs_tuners_ins.ignore_nice) { /* nothing to do */ > > - mutex_unlock(&dbs_mutex); > > + if (input == dbs_tuners_ins.ignore_nice) /* nothing to do */ > > return count; > > - } > > + > > dbs_tuners_ins.ignore_nice = input; > > > > /* we need to re-evaluate prev_cpu_idle */ > > @@ -332,8 +307,6 @@ static ssize_t store_ignore_nice_load(struct > > cpufreq_policy *policy, dbs_info->prev_cpu_nice = > > kstat_cpu(j).cpustat.nice; > > > > } > > - mutex_unlock(&dbs_mutex); > > - > > return count; > > } > > > > @@ -350,10 +323,8 @@ static ssize_t store_powersave_bias(struct > > cpufreq_policy *unused, if (input > 1000) > > input = 1000; > > > > - mutex_lock(&dbs_mutex); > > dbs_tuners_ins.powersave_bias = input; > > ondemand_powersave_bias_init(); > > - mutex_unlock(&dbs_mutex); > > > > return count; > > } > > @@ -586,13 +557,11 @@ static int cpufreq_governor_dbs(struct > > cpufreq_policy *policy, if (this_dbs_info->enable) /* Already enabled */ > > break; > > > > - mutex_lock(&dbs_mutex); > > dbs_enable++; > > > > rc = sysfs_create_group(&policy->kobj, &dbs_attr_group); > > if (rc) { > > dbs_enable--; > > - mutex_unlock(&dbs_mutex); > > return rc; > > } > > > > @@ -627,28 +596,21 @@ static int cpufreq_governor_dbs(struct > > cpufreq_policy *policy, dbs_tuners_ins.sampling_rate = def_sampling_rate; > > } > > dbs_timer_init(this_dbs_info); > > - > > - mutex_unlock(&dbs_mutex); > > break; > > > > case CPUFREQ_GOV_STOP: > > - mutex_lock(&dbs_mutex); > > dbs_timer_exit(this_dbs_info); > > sysfs_remove_group(&policy->kobj, &dbs_attr_group); > > dbs_enable--; > > - mutex_unlock(&dbs_mutex); > > - > > break; > > > > case CPUFREQ_GOV_LIMITS: > > - mutex_lock(&dbs_mutex); > > if (policy->max < this_dbs_info->cur_policy->cur) > > __cpufreq_driver_target(this_dbs_info->cur_policy, > > policy->max, CPUFREQ_RELATION_H); > > else if (policy->min > this_dbs_info->cur_policy->cur) > > __cpufreq_driver_target(this_dbs_info->cur_policy, > > policy->min, CPUFREQ_RELATION_L); > > - mutex_unlock(&dbs_mutex); > > break; > > } > > return 0; > > -- > > 1.6.0.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/