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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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