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Subject[PATCH 1/2] CPUFREQ: Remove unneeded dbs_mutexes from ondemand and conservative governors
Date
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 <venkatesh.pallipadi@intel.com>
Signed-off-by: Thomas Renninger <trenn@suse.de>
---
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 <linux/cpu.h>
#include <linux/jiffies.h>
#include <linux/kernel_stat.h>
-#include <linux/mutex.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/ktime.h>
@@ -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);
-
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,
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 <linux/cpu.h>
#include <linux/jiffies.h>
#include <linux/kernel_stat.h>
-#include <linux/mutex.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/ktime.h>
@@ -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


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