Message-ID: <9f5c7de3-dd03-5c0a-ea97-bc170303422b@samsung.com>
Date:   Tue, 10 Dec 2019 18:25:16 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Kamil Konieczny <k.konieczny@...sung.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>
Subject: Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

On 12/10/19 6:03 PM, Kamil Konieczny wrote:
> Hi Chanwoo,
> 
> On 10.12.2019 02:47, Chanwoo Choi wrote:
>> 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.
> 
> Unfortunatly I do not have such tests. Do you have them ?
> May you share them with me or Marek ?

You have to do some test for this patch
because you tried to use the 'delayed work' by this patch.

Actually, If possible, I want to apply some feature
if there are any real requirements.

> 
>> 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. 
> 
> sysfs allows change in runtime

hmm. I don't say that sysfs can't change the value at the runtime.
It is not proper answer from my opinion. Without any answer
from my opinion, you just say the feature of sysfs interface.
You and me already knew that user can change the value via sysfs.

> 
>> 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.
> 
> Good point, performance or powersave with fixed max or min freq
> do not need them.
> 
>> If you suggest the reasonable data with test result,
>> I prefer to add the new flag to 'struct devfreq_dev_profile'.
> 
> imho users of devfreq may give it a try and perform tests themselfs
> and then share results.

As I commented above, I want to apply some feature
if there are any real requirements.

> 
>>>
>>> Signed-off-by: Kamil Konieczny <k.konieczny@...sung.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@...sung.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@...aro.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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