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SubjectRe: [PATCH 2/4] PM / devfreq: add possibility for delayed work
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On 12/9/19 11:44 PM, Kamil Konieczny wrote:
> Current devfreq workqueue uses deferred timer. Introduce sysfs
> file delayed_timer and use it for change from deferred to
> delayed work. The default is to use old deferred one, which
> saves power, but can miss increased demand for higher bus
> frequency if timer was assigned to idle cpu.

As I commented on patch1, If you hope to change the feature
related to both performance and power-consumption,
you have to suggest the reasonable data with test result
on multiple scenarios.

Firstly,
I don't agree to add 'delayed_timer' sysfs entries.
If some device driver want to use the different type of
workqueue, they can choice the workqueue type in the
probe function of device driver.

Secondly, the 'dealyed_timer' is not for all devfreq
device driver. Only devfreq device driver uses the
'simple_ondemand' governor. It is wrong to show
without any specific reason.


If you suggest the reasonable data with test result,
I prefer to add the new flag to 'struct devfreq_dev_profile'.

>
> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
> ---
> Documentation/ABI/testing/sysfs-class-devfreq | 10 ++++
> drivers/devfreq/devfreq.c | 46 ++++++++++++++++++-
> include/linux/devfreq.h | 2 +
> 3 files changed, 57 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-class-devfreq b/Documentation/ABI/testing/sysfs-class-devfreq
> index 9758eb85ade3..07bfd0df6a4a 100644
> --- a/Documentation/ABI/testing/sysfs-class-devfreq
> +++ b/Documentation/ABI/testing/sysfs-class-devfreq
> @@ -30,6 +30,16 @@ Description:
> target_freq when get_cur_freq() is not implemented by
> devfreq driver.
>
> +What: /sys/class/devfreq/.../delayed_timer
> +Date: December 2019
> +Contact: Kamil Konieczny <k.konieczny@samsung.com>
> +Description:
> + This ABI shows or clears timer type used by devfreq
> + workqueue. When 0, it uses default deferred timer.
> + When set to 1 devfreq will use delayed timer. Example
> + useage:
> + echo 1 > /sys/class/devfreq/.../delayed_timer
> +
> What: /sys/class/devfreq/.../target_freq
> Date: September 2012
> Contact: Rajagopal Venkat <rajagopal.venkat@linaro.org>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 955949c6fc1f..c277d1770fef 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -445,7 +445,11 @@ void devfreq_monitor_start(struct devfreq *devfreq)
> if (devfreq->governor->interrupt_driven)
> return;
>
> - INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
> + if (devfreq->delayed_timer)
> + INIT_DELAYED_WORK(&devfreq->work, devfreq_monitor);
> + else
> + INIT_DEFERRABLE_WORK(&devfreq->work, devfreq_monitor);
> +
> if (devfreq->profile->polling_ms)
> queue_delayed_work(devfreq_wq, &devfreq->work,
> msecs_to_jiffies(devfreq->profile->polling_ms));
> @@ -698,6 +702,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
> devfreq->last_status.current_frequency = profile->initial_freq;
> devfreq->data = data;
> devfreq->nb.notifier_call = devfreq_notifier_call;
> + devfreq->delayed_timer = false;
>
> if (!devfreq->profile->max_state && !devfreq->profile->freq_table) {
> mutex_unlock(&devfreq->lock);
> @@ -1288,6 +1293,44 @@ static ssize_t available_governors_show(struct device *d,
> }
> static DEVICE_ATTR_RO(available_governors);
>
> +static ssize_t delayed_timer_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + int i;
> +
> + i = to_devfreq(dev)->delayed_timer ? 1 : 0;
> + return sprintf(buf, "%d\n", i);
> +}
> +
> +static ssize_t delayed_timer_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct devfreq *df = to_devfreq(dev);
> + bool old_timer;
> + int value, ret;
> +
> + if (!df->governor)
> + return -EINVAL;
> +
> + ret = kstrtoint(buf, 10, &value);
> + if (ret || (value != 1 && value != 0))
> + return -EINVAL;
> +
> + mutex_lock(&df->lock);
> + old_timer = df->delayed_timer;
> + df->delayed_timer = value == 0 ? false : true;
> + mutex_unlock(&df->lock);
> +
> + if (old_timer != df->delayed_timer) {
> + devfreq_monitor_stop(df);
> + devfreq_monitor_start(df);
> + }
> +
> + return count;
> +}
> +static DEVICE_ATTR_RW(delayed_timer);
> +
> static ssize_t cur_freq_show(struct device *dev, struct device_attribute *attr,
> char *buf)
> {
> @@ -1513,6 +1556,7 @@ static struct attribute *devfreq_attrs[] = {
> &dev_attr_name.attr,
> &dev_attr_governor.attr,
> &dev_attr_available_governors.attr,
> + &dev_attr_delayed_timer.attr,
> &dev_attr_cur_freq.attr,
> &dev_attr_available_frequencies.attr,
> &dev_attr_target_freq.attr,
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index de2fdc56aa5b..761aa0a09db7 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -134,6 +134,7 @@ struct devfreq_stats {
> * reevaluate operable frequencies. Devfreq users may use
> * devfreq.nb to the corresponding register notifier call chain.
> * @work: delayed work for load monitoring.
> + * @delayed_timer: use delayed or deferred timer for workqueue.
> * @previous_freq: previously configured frequency value.
> * @data: Private data of the governor. The devfreq framework does not
> * touch this.
> @@ -166,6 +167,7 @@ struct devfreq {
> char governor_name[DEVFREQ_NAME_LEN];
> struct notifier_block nb;
> struct delayed_work work;
> + bool delayed_timer;
>
> unsigned long previous_freq;
> struct devfreq_dev_status last_status;
>


--
Best Regards,
Chanwoo Choi
Samsung Electronics

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