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SubjectRe: [PATCH 1/2] PM / devfreq: add min/max_freq limit requested by users.
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On Thu, Jan 12, 2012 at 9:20 AM, Turquette, Mike <mturquette@ti.com> wrote:
> On Wed, Jan 11, 2012 at 2:02 AM, MyungJoo Ham <myungjoo.ham@samsung.com> wrote:
>> The frequency requested to devfreq device driver from devfreq governors
>> is restricted by min_freq and max_freq input.
>
> Hello MyungJoo,
>
> This change appears to allow userspace to set min/max limits on
> devfreq devices via sysfs.  Not everyone likes to expose this stuff
> (similar to the discussions around controlling clocks from debugfs).
>
> Should it be wrapped in some new config option?  I think a sane
> default is that if the sysfs config option for devfreq is selected
> then it should include all of the read-only stuff.  A second config
> option (which depends on the option in my previous sentence) should
> allow the read-write stuff to be enabled separately.  Thoughts?
>
> Also, how are you using this feature in practice?  Is this just for
> test or are you planning on more fine-grained control of device
> frequencies from userspace?
>
> Mike

Hello Mike,


Although turning off clocks inconsiderately usually crashes the
system, setting min/max frequencies generally affects (if not always)
only the performance and power consumption.

For the optional min/max freq, I think each device should be able to
choose to use it or not. Thus, rather than adding a Kconfig option,
I'll let "profile" (struct devfreq_dev_profile) include
"expose_user_min_max_freq" option.

In practice, we have been using min/max to test DVFS behaviors and its
side effects. And we are going to use them to 1. restrict power
consumption forcibly by the platform software if it is too hot or the
battery is low, and to 2. guarantee the minimum performance for
specific tasks controlled by the platform software.

Anyway, the reason 2 could be tackled by pm-qos if we allow more
options in pm-qos with 1. pm qos type to enforce DVFS response time.
2. pm qos type to enforce graphics performance. And adding a duration
option to pm-qos requests will be helpful (sort of a helper function):
i.e., pm_qos_timed_request(struct pm_qos_request *req, int
pm_qos_class, s32 value, unsigned long duration_ms);



Cheers!
MyungJoo.


>
>>
>> Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
>> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
>> ---
>>  drivers/devfreq/devfreq.c                 |   70 +++++++++++++++++++++++++++++
>>  drivers/devfreq/governor_performance.c    |    5 ++-
>>  drivers/devfreq/governor_powersave.c      |    2 +-
>>  drivers/devfreq/governor_simpleondemand.c |   12 ++++-
>>  drivers/devfreq/governor_userspace.c      |   15 +++++-
>>  include/linux/devfreq.h                   |    5 ++
>>  6 files changed, 101 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 59d24e9..358d129 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -502,12 +502,82 @@ static ssize_t show_central_polling(struct device *dev,
>>                       !to_devfreq(dev)->governor->no_central_polling);
>>  }
>>
>> +static ssize_t store_min_freq(struct device *dev, struct device_attribute *attr,
>> +                             const char *buf, size_t count)
>> +{
>> +       struct devfreq *df = to_devfreq(dev);
>> +       unsigned long value;
>> +       int ret;
>> +       unsigned long max;
>> +
>> +       ret = sscanf(buf, "%lu", &value);
>> +       if (ret != 1)
>> +               goto out;
>> +
>> +       mutex_lock(&df->lock);
>> +       max = df->max_freq;
>> +       if (value && max && value > max) {
>> +               ret = -EINVAL;
>> +               goto unlock;
>> +       }
>> +
>> +       df->min_freq = value;
>> +       update_devfreq(df);
>> +       ret = count;
>> +unlock:
>> +       mutex_unlock(&df->lock);
>> +out:
>> +       return ret;
>> +}
>> +
>> +static ssize_t show_min_freq(struct device *dev, struct device_attribute *attr,
>> +                            char *buf)
>> +{
>> +       return sprintf(buf, "%lu\n", to_devfreq(dev)->min_freq);
>> +}
>> +
>> +static ssize_t store_max_freq(struct device *dev, struct device_attribute *attr,
>> +                             const char *buf, size_t count)
>> +{
>> +       struct devfreq *df = to_devfreq(dev);
>> +       unsigned long value;
>> +       int ret;
>> +       unsigned long min;
>> +
>> +       ret = sscanf(buf, "%lu", &value);
>> +       if (ret != 1)
>> +               goto out;
>> +
>> +       mutex_lock(&df->lock);
>> +       min = df->min_freq;
>> +       if (value && min && value < min) {
>> +               ret = -EINVAL;
>> +               goto unlock;
>> +       }
>> +
>> +       df->max_freq = value;
>> +       update_devfreq(df);
>> +       ret = count;
>> +unlock:
>> +       mutex_unlock(&df->lock);
>> +out:
>> +       return ret;
>> +}
>> +
>> +static ssize_t show_max_freq(struct device *dev, struct device_attribute *attr,
>> +                            char *buf)
>> +{
>> +       return sprintf(buf, "%lu\n", to_devfreq(dev)->max_freq);
>> +}
>> +
>>  static struct device_attribute devfreq_attrs[] = {
>>        __ATTR(governor, S_IRUGO, show_governor, NULL),
>>        __ATTR(cur_freq, S_IRUGO, show_freq, NULL),
>>        __ATTR(central_polling, S_IRUGO, show_central_polling, NULL),
>>        __ATTR(polling_interval, S_IRUGO | S_IWUSR, show_polling_interval,
>>               store_polling_interval),
>> +       __ATTR(min_freq, S_IRUGO | S_IWUSR, show_min_freq, store_min_freq),
>> +       __ATTR(max_freq, S_IRUGO | S_IWUSR, show_max_freq, store_max_freq),
>>        { },
>>  };
>>
>> diff --git a/drivers/devfreq/governor_performance.c b/drivers/devfreq/governor_performance.c
>> index c0596b2..574a06b 100644
>> --- a/drivers/devfreq/governor_performance.c
>> +++ b/drivers/devfreq/governor_performance.c
>> @@ -18,7 +18,10 @@ static int devfreq_performance_func(struct devfreq *df,
>>         * target callback should be able to get floor value as
>>         * said in devfreq.h
>>         */
>> -       *freq = UINT_MAX;
>> +       if (!df->max_freq)
>> +               *freq = UINT_MAX;
>> +       else
>> +               *freq = df->max_freq;
>>        return 0;
>>  }
>>
>> diff --git a/drivers/devfreq/governor_powersave.c b/drivers/devfreq/governor_powersave.c
>> index 2483a85..d742d4a 100644
>> --- a/drivers/devfreq/governor_powersave.c
>> +++ b/drivers/devfreq/governor_powersave.c
>> @@ -18,7 +18,7 @@ static int devfreq_powersave_func(struct devfreq *df,
>>         * target callback should be able to get ceiling value as
>>         * said in devfreq.h
>>         */
>> -       *freq = 0;
>> +       *freq = df->min_freq;
>>        return 0;
>>  }
>>
>> diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
>> index efad8dc..a2e3eae 100644
>> --- a/drivers/devfreq/governor_simpleondemand.c
>> +++ b/drivers/devfreq/governor_simpleondemand.c
>> @@ -25,6 +25,7 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>        unsigned int dfso_upthreshold = DFSO_UPTHRESHOLD;
>>        unsigned int dfso_downdifferential = DFSO_DOWNDIFFERENCTIAL;
>>        struct devfreq_simple_ondemand_data *data = df->data;
>> +       unsigned long max = (df->max_freq) ? df->max_freq : UINT_MAX;
>>
>>        if (err)
>>                return err;
>> @@ -41,7 +42,7 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>
>>        /* Assume MAX if it is going to be divided by zero */
>>        if (stat.total_time == 0) {
>> -               *freq = UINT_MAX;
>> +               *freq = max;
>>                return 0;
>>        }
>>
>> @@ -54,13 +55,13 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>        /* Set MAX if it's busy enough */
>>        if (stat.busy_time * 100 >
>>            stat.total_time * dfso_upthreshold) {
>> -               *freq = UINT_MAX;
>> +               *freq = max;
>>                return 0;
>>        }
>>
>>        /* Set MAX if we do not know the initial frequency */
>>        if (stat.current_frequency == 0) {
>> -               *freq = UINT_MAX;
>> +               *freq = max;
>>                return 0;
>>        }
>>
>> @@ -79,6 +80,11 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>        b = div_u64(b, (dfso_upthreshold - dfso_downdifferential / 2));
>>        *freq = (unsigned long) b;
>>
>> +       if (df->min_freq && *freq < df->min_freq)
>> +               *freq = df->min_freq;
>> +       if (df->max_freq && *freq > df->max_freq)
>> +               *freq = df->max_freq;
>> +
>>        return 0;
>>  }
>>
>> diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
>> index 4f8b563..0681246 100644
>> --- a/drivers/devfreq/governor_userspace.c
>> +++ b/drivers/devfreq/governor_userspace.c
>> @@ -25,10 +25,19 @@ static int devfreq_userspace_func(struct devfreq *df, unsigned long *freq)
>>  {
>>        struct userspace_data *data = df->data;
>>
>> -       if (!data->valid)
>> +       if (data->valid) {
>> +               unsigned long adjusted_freq = data->user_frequency;
>> +
>> +               if (df->max_freq && adjusted_freq > df->max_freq)
>> +                       adjusted_freq = df->max_freq;
>> +
>> +               if (df->min_freq && adjusted_freq < df->min_freq)
>> +                       adjusted_freq = df->min_freq;
>> +
>> +               *freq = adjusted_freq;
>> +       } else {
>>                *freq = df->previous_freq; /* No user freq specified yet */
>> -       else
>> -               *freq = data->user_frequency;
>> +       }
>>        return 0;
>>  }
>>
>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>> index 98ce812..e9385bf 100644
>> --- a/include/linux/devfreq.h
>> +++ b/include/linux/devfreq.h
>> @@ -124,6 +124,8 @@ struct devfreq_governor {
>>  *             touch this.
>>  * @being_removed      a flag to mark that this object is being removed in
>>  *                     order to prevent trying to remove the object multiple times.
>> + * @min_freq   Limit minimum frequency requested by user (0: none)
>> + * @max_freq   Limit maximum frequency requested by user (0: none)
>>  *
>>  * This structure stores the devfreq information for a give device.
>>  *
>> @@ -149,6 +151,9 @@ struct devfreq {
>>        void *data; /* private data for governors */
>>
>>        bool being_removed;
>> +
>> +       unsigned long min_freq;
>> +       unsigned long max_freq;
>>  };
>>
>>  #if defined(CONFIG_PM_DEVFREQ)
>> --
>> 1.7.4.1
>>



--
MyungJoo Ham, Ph.D.
Mobile Software Platform Lab, DMC Business, Samsung Electronics
--
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