[PATCH 0/4] PM / devfreq: add possibility for delayed work

[PATCH 0/4] PM / devfreq: add possibility for delayed work

[Kamil Konieczny]

Add possibility for changing work from deferred to delayed in devfreq
workqueue. This can be done with

echo 1 > /sys/class/devfreq/devfreqX/delayed_timer

Second way is to use config option, in that case delayed timer will be
used from devfreq start.

Default behaviour is to stick with old delayed timer.

This patchset was inspired by Lukasz Luba patches and discussion that
follows, see

[v1] https://marc.info/?l=linux-pm&m=154904631226997&w=2
[v2] https://marc.info/?l=linux-pm&m=154989907416072&w=2
[v3] https://marc.info/?l=linux-pm&m=155001027823904&w=2

Kamil Konieczny (4):
  PM / devfreq: reuse system workqueue machanism
  PM / devfreq: add possibility for delayed work
  PM / devfreq: Kconfig: add DEVFREQ_DELAYED_TIMER option
  PM / devfreq: use delayed work if DEVFREQ_DELAYED_TIMER set

 Documentation/ABI/testing/sysfs-class-devfreq | 10 ++++
 drivers/devfreq/Kconfig                       | 12 ++++
 drivers/devfreq/devfreq.c                     | 55 +++++++++++++++++--
 include/linux/devfreq.h                       |  2 +
 4 files changed, 75 insertions(+), 4 deletions(-)

-- 
2.24.0

[PATCH 1/4] PM / devfreq: reuse system workqueue machanism

[Kamil Konieczny]

There is no need for creating another workqueue, it is enough
to reuse system_freezable_power_efficient one.

Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
---
 drivers/devfreq/devfreq.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 46a7ff7c2994..955949c6fc1f 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
 		return PTR_ERR(devfreq_class);
 	}
 
-	devfreq_wq = create_freezable_workqueue("devfreq_wq");
+	devfreq_wq = system_freezable_power_efficient_wq;
 	if (!devfreq_wq) {
 		class_destroy(devfreq_class);
-		pr_err("%s: couldn't create workqueue\n", __FILE__);
-		return -ENOMEM;
+		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
+		return -EINVAL;
 	}
 	devfreq_class->dev_groups = devfreq_groups;
 
-- 
2.24.0

[PATCH 2/4] PM / devfreq: add possibility for delayed work

[Kamil Konieczny]

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.

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;
-- 
2.24.0

[PATCH 3/4] PM / devfreq: Kconfig: add DEVFREQ_DELAYED_TIMER option

[Kamil Konieczny]

Add Kconfig option DEVFREQ_DELAYED_TIMER. If set, devfreq workqueue
will use delayed timer from its start.

Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
---
 drivers/devfreq/Kconfig | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
index 38a94df749a2..c799917c34c9 100644
--- a/drivers/devfreq/Kconfig
+++ b/drivers/devfreq/Kconfig
@@ -74,6 +74,18 @@ config DEVFREQ_GOV_PASSIVE
 	  through sysfs entries. The passive governor recommends that
 	  devfreq device uses the OPP table to get the frequency/voltage.
 
+comment "DEVFREQ Options"
+
+config DEVFREQ_DELAYED_TIMER
+	bool "Use delayed timer in Simple Ondemand Governor"
+	default false
+	help
+	  Simple Ondemand Governor uses polling for reading buses counters.
+	  A default timer used is deferred, which saves power, but can
+	  miss increased demand for higher bus frequency if timer was
+	  assigned to idle cpu. If you want to change this to delayed
+	  timer at the cost of more power used, say Yes here.
+
 comment "DEVFREQ Drivers"
 
 config ARM_EXYNOS_BUS_DEVFREQ
-- 
2.24.0

[PATCH 4/4] PM / devfreq: use delayed work if DEVFREQ_DELAYED_TIMER set

[Kamil Konieczny]

If option DEVFREQ_DELAYED_TIMER is set use delayed work in devfreq
workqueue from devfreq start.

Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
---
 drivers/devfreq/devfreq.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index c277d1770fef..d9edf648a09e 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -702,7 +702,10 @@ 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 (IS_ENABLED(CONFIG_DEVFREQ_DELAYED_TIMER))
+		devfreq->delayed_timer = true;
+	else
+		devfreq->delayed_timer = false;
 
 	if (!devfreq->profile->max_state && !devfreq->profile->freq_table) {
 		mutex_unlock(&devfreq->lock);
-- 
2.24.0

Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

[Matthias Kaehlcke]

Hi,

On Mon, Dec 09, 2019 at 03:44:23PM +0100, 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.
> 
> 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;

devfreq is zero initialized (allocated with kzalloc()), hence this is
unnecessary.

>  
>  	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);

get rid of 'i' and just use df->delayed_timer in sprintf().

> +}
> +
> +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;

Not a great name, the variable doesn't hold a timer. I'd suggest something
like 'prev_val'.

> +	int value, ret;
> +
> +	if (!df->governor)
> +		return -EINVAL;
> +
> +	ret = kstrtoint(buf, 10, &value);
> +	if (ret || (value != 1 && value != 0))
> +		return -EINVAL;

use kstrtobool() instead of partially re-implementing it.

> +
> +	mutex_lock(&df->lock);
> +	old_timer = df->delayed_timer;
> +	df->delayed_timer = value == 0 ? false : true;

What's wrong with:

df->delayed_timer = value;

?

> +	mutex_unlock(&df->lock);

Does the locking as is actually provide any value? The use case seems to
be concurrent setting of the sysfs attribute. The lock is released after
the assignment, hence the value of 'df->delayed_timer' could be overwritten
before the condition below is evaluated.

If you want to protect against this case you need something like this:

// don't release the lock before evaluating the condition

> +	if (old_timer != df->delayed_timer) {
  	   	mutex_unlock(&df->lock);
> +		devfreq_monitor_stop(df);
> +		devfreq_monitor_start(df);
> +	}
  	else {
		mutex_unlock(&df->lock);
	}

I don't pretend it's pretty ;-)

Re: [PATCH 3/4] PM / devfreq: Kconfig: add DEVFREQ_DELAYED_TIMER option

[Matthias Kaehlcke]

On Mon, Dec 09, 2019 at 03:44:24PM +0100, Kamil Konieczny wrote:
> Add Kconfig option DEVFREQ_DELAYED_TIMER. If set, devfreq workqueue
> will use delayed timer from its start.

s/from its start/by default/

> 
> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
> ---
>  drivers/devfreq/Kconfig | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index 38a94df749a2..c799917c34c9 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -74,6 +74,18 @@ config DEVFREQ_GOV_PASSIVE
>  	  through sysfs entries. The passive governor recommends that
>  	  devfreq device uses the OPP table to get the frequency/voltage.
>  
> +comment "DEVFREQ Options"
> +
> +config DEVFREQ_DELAYED_TIMER
> +	bool "Use delayed timer in Simple Ondemand Governor"

Is the use really limited to the Simple Ondemand Governor? I don't think
so, at least the Tegra devfreq driver also does monitoring and others
might follow.


> +	default false
> +	help
> +	  Simple Ondemand Governor uses polling for reading buses counters.
> +	  A default timer used is deferred, which saves power, but can
> +	  miss increased demand for higher bus frequency if timer was
> +	  assigned to idle cpu. If you want to change this to delayed
> +	  timer at the cost of more power used, say Yes here.
> +
>  comment "DEVFREQ Drivers"
>  
>  config ARM_EXYNOS_BUS_DEVFREQ


This patch on it's own does nothing. Squash it with '[4/4] PM / devfreq:
use delayed work if DEVFREQ_DELAYED_TIMER set'.

Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

[Chanwoo Choi]

On 12/9/19 11:44 PM, Kamil Konieczny wrote:
> There is no need for creating another workqueue, it is enough
> to reuse system_freezable_power_efficient one.
> 
> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
> ---
>  drivers/devfreq/devfreq.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 46a7ff7c2994..955949c6fc1f 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
>  		return PTR_ERR(devfreq_class);
>  	}
>  
> -	devfreq_wq = create_freezable_workqueue("devfreq_wq");
> +	devfreq_wq = system_freezable_power_efficient_wq;

It affect the behaviors of whole device drivers using devfreq subsystem.
It is not good to change the workqueue type without any reasonable
data like experiment result, power-consumption result and performance
result for almost device drivers using devfreq subsystem.

Are there any problem or any benefit to change workqueue type?

Actually, it is not simple to change the like just one device driver
because devfreq subsytem is very important for both performance
and power-consumption.

If you hope to change the feature related to both performance 
and power-consumption, please suggest the reasonable data
with fundamental reason.

So, I can't agree it.


>  	if (!devfreq_wq) {
>  		class_destroy(devfreq_class);
> -		pr_err("%s: couldn't create workqueue\n", __FILE__);
> -		return -ENOMEM;
> +		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
> +		return -EINVAL;
>  	}
>  	devfreq_class->dev_groups = devfreq_groups;
>  
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

[Chanwoo Choi]

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

Re: [PATCH 3/4] PM / devfreq: Kconfig: add DEVFREQ_DELAYED_TIMER option

[Chanwoo Choi]

On 12/9/19 11:44 PM, Kamil Konieczny wrote:
> Add Kconfig option DEVFREQ_DELAYED_TIMER. If set, devfreq workqueue
> will use delayed timer from its start.
> 
> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
> ---
>  drivers/devfreq/Kconfig | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
> index 38a94df749a2..c799917c34c9 100644
> --- a/drivers/devfreq/Kconfig
> +++ b/drivers/devfreq/Kconfig
> @@ -74,6 +74,18 @@ config DEVFREQ_GOV_PASSIVE
>  	  through sysfs entries. The passive governor recommends that
>  	  devfreq device uses the OPP table to get the frequency/voltage.
>  
> +comment "DEVFREQ Options"
> +
> +config DEVFREQ_DELAYED_TIMER
> +	bool "Use delayed timer in Simple Ondemand Governor"
> +	default false
> +	help
> +	  Simple Ondemand Governor uses polling for reading buses counters.
> +	  A default timer used is deferred, which saves power, but can
> +	  miss increased demand for higher bus frequency if timer was
> +	  assigned to idle cpu. If you want to change this to delayed
> +	  timer at the cost of more power used, say Yes here.
> +
>  comment "DEVFREQ Drivers"

I don't think that we cannot choice the all options in Kconfig
at the build time. If we add something like this patch,

we can choice the any options in Kconfig as following:
- polling time (millisecond)
- up threshold
- down threshold
- type of workqueue
- etc ...

Also, there are too much optional value and selectable value 
in the linux kernel. 

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

>  
>  config ARM_EXYNOS_BUS_DEVFREQ
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

[Kamil Konieczny]

On 10.12.2019 02:41, Chanwoo Choi wrote:
> On 12/9/19 11:44 PM, Kamil Konieczny wrote:
>> There is no need for creating another workqueue, it is enough
>> to reuse system_freezable_power_efficient one.
>>
>> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
>> ---
>>  drivers/devfreq/devfreq.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 46a7ff7c2994..955949c6fc1f 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
>>  		return PTR_ERR(devfreq_class);
>>  	}
>>  
>> -	devfreq_wq = create_freezable_workqueue("devfreq_wq");
>> +	devfreq_wq = system_freezable_power_efficient_wq;
> 
> It affect the behaviors of whole device drivers using devfreq subsystem.
> It is not good to change the workqueue type without any reasonable
> data like experiment result, power-consumption result and performance
> result for almost device drivers using devfreq subsystem.
> 
> Are there any problem or any benefit to change workqueue type?

The workqueue is freezable with additional capability of 'power_efficient',
it is already developed by linux community so why not reuse it ?

> Actually, it is not simple to change the like just one device driver
> because devfreq subsytem is very important for both performance
> and power-consumption.

I agree. The name of this wq promises what you want, both freezable
and power efficiency.

> If you hope to change the feature related to both performance 
> and power-consumption, please suggest the reasonable data
> with fundamental reason.
> 
> So, I can't agree it.
> 
> 
>>  	if (!devfreq_wq) {
>>  		class_destroy(devfreq_class);
>> -		pr_err("%s: couldn't create workqueue\n", __FILE__);
>> -		return -ENOMEM;
>> +		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
>> +		return -EINVAL;
>>  	}
>>  	devfreq_class->dev_groups = devfreq_groups;
>>  
>>
> 
> 

-- 
Best regards,
Kamil Konieczny
Samsung R&D Institute Poland

Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

[Chanwoo Choi]

On 12/10/19 4:28 PM, Kamil Konieczny wrote:
> On 10.12.2019 02:41, Chanwoo Choi wrote:
>> On 12/9/19 11:44 PM, Kamil Konieczny wrote:
>>> There is no need for creating another workqueue, it is enough
>>> to reuse system_freezable_power_efficient one.
>>>
>>> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
>>> ---
>>>  drivers/devfreq/devfreq.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 46a7ff7c2994..955949c6fc1f 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
>>>  		return PTR_ERR(devfreq_class);
>>>  	}
>>>  
>>> -	devfreq_wq = create_freezable_workqueue("devfreq_wq");
>>> +	devfreq_wq = system_freezable_power_efficient_wq;
>>
>> It affect the behaviors of whole device drivers using devfreq subsystem.
>> It is not good to change the workqueue type without any reasonable
>> data like experiment result, power-consumption result and performance
>> result for almost device drivers using devfreq subsystem.
>>
>> Are there any problem or any benefit to change workqueue type?
> 
> The workqueue is freezable with additional capability of 'power_efficient',
> it is already developed by linux community so why not reuse it ?

As you agreed below, why don't you suggest the any reasonable test result
with this patch? As I commented, it affects the all device drivers. 
It is necessary to suggest the test result on multiple scenarios
in order to prevent the any power-consumption and performance regression.
It is not easy to change them without any data.

Frankly, if you test almost scenarios and suggest the reasonable result
that anyone can understand, like there are never difference
between "create_freezable_workqueue("devfreq_wq");" and system_freezable_power_efficient_wq.
But you don't suggest any data.

- The original devfreq_wq include the only work related to devfreq.
- system_freezable_power_efficient_wq include the all works registered
from both other subsystem and device drivers in linux kernel.

> 
>> Actually, it is not simple to change the like just one device driver
>> because devfreq subsytem is very important for both performance
>> and power-consumption.
> 
> I agree. The name of this wq promises what you want, both freezable
> and power efficiency.
> 
>> If you hope to change the feature related to both performance 
>> and power-consumption, please suggest the reasonable data
>> with fundamental reason.
>>
>> So, I can't agree it.
>>
>>
>>>  	if (!devfreq_wq) {
>>>  		class_destroy(devfreq_class);
>>> -		pr_err("%s: couldn't create workqueue\n", __FILE__);
>>> -		return -ENOMEM;
>>> +		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
>>> +		return -EINVAL;
>>>  	}
>>>  	devfreq_class->dev_groups = devfreq_groups;
>>>  
>>>
>>
>>
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

[Kamil Konieczny]

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 ?

> 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

> 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.

>>
>> 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,
Kamil Konieczny
Samsung R&D Institute Poland

Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

[Chanwoo Choi]

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@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

Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

[Kamil Konieczny]

Hi Chanwoo,

On 10.12.2019 08:53, Chanwoo Choi wrote:
> On 12/10/19 4:28 PM, Kamil Konieczny wrote:
>> On 10.12.2019 02:41, Chanwoo Choi wrote:
>>> On 12/9/19 11:44 PM, Kamil Konieczny wrote:
>>>> There is no need for creating another workqueue, it is enough
>>>> to reuse system_freezable_power_efficient one.
>>>>
>>>> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
>>>> ---
>>>>  drivers/devfreq/devfreq.c | 6 +++---
>>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>> index 46a7ff7c2994..955949c6fc1f 100644
>>>> --- a/drivers/devfreq/devfreq.c
>>>> +++ b/drivers/devfreq/devfreq.c
>>>> @@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
>>>>  		return PTR_ERR(devfreq_class);
>>>>  	}
>>>>  
>>>> -	devfreq_wq = create_freezable_workqueue("devfreq_wq");
>>>> +	devfreq_wq = system_freezable_power_efficient_wq;
>>>
>>> It affect the behaviors of whole device drivers using devfreq subsystem.
>>> It is not good to change the workqueue type without any reasonable
>>> data like experiment result, power-consumption result and performance
>>> result for almost device drivers using devfreq subsystem.
>>>
>>> Are there any problem or any benefit to change workqueue type?
>>
>> The workqueue is freezable with additional capability of 'power_efficient',
>> it is already developed by linux community so why not reuse it ?
> 
> As you agreed below, why don't you suggest the any reasonable test result
> with this patch? As I commented, it affects the all device drivers. 
> It is necessary to suggest the test result on multiple scenarios
> in order to prevent the any power-consumption and performance regression.
> It is not easy to change them without any data.
> 
> Frankly, if you test almost scenarios and suggest the reasonable result
> that anyone can understand, like there are never difference
> between "create_freezable_workqueue("devfreq_wq");" and system_freezable_power_efficient_wq.
> But you don't suggest any data.

I agree about tests data needed for deciding about change. As I already wrote in other
letter, I do not have such tests procedures, so if you have them and you may share
them with me or Marek, I can run them and gather tests results.

> - The original devfreq_wq include the only work related to devfreq.
> - system_freezable_power_efficient_wq include the all works registered
> from both other subsystem and device drivers in linux kernel.

I do not know that good system wq, devfreq_wq have only one work item so
imho it is not beneficial to use separate wq. Seperate wq can be good
during debugging problems with wq.

>>> Actually, it is not simple to change the like just one device driver
>>> because devfreq subsytem is very important for both performance
>>> and power-consumption.
>>
>> I agree. The name of this wq promises what you want, both freezable
>> and power efficiency.
>>
>>> If you hope to change the feature related to both performance 
>>> and power-consumption, please suggest the reasonable data
>>> with fundamental reason.
>>>
>>> So, I can't agree it.
>>>
>>>
>>>>  	if (!devfreq_wq) {
>>>>  		class_destroy(devfreq_class);
>>>> -		pr_err("%s: couldn't create workqueue\n", __FILE__);
>>>> -		return -ENOMEM;
>>>> +		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
>>>> +		return -EINVAL;
>>>>  	}
>>>>  	devfreq_class->dev_groups = devfreq_groups;

-- 
Best regards,
Kamil Konieczny
Samsung R&D Institute Poland

Re: [PATCH 3/4] PM / devfreq: Kconfig: add DEVFREQ_DELAYED_TIMER option

[Kamil Konieczny]

Hi,

On 09.12.2019 20:34, Matthias Kaehlcke wrote:
> On Mon, Dec 09, 2019 at 03:44:24PM +0100, Kamil Konieczny wrote:
>> Add Kconfig option DEVFREQ_DELAYED_TIMER. If set, devfreq workqueue
>> will use delayed timer from its start.
> 
> s/from its start/by default/
> 

thank you for review, I will correct this

>>
>> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
>> ---
>>  drivers/devfreq/Kconfig | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>>
>> diff --git a/drivers/devfreq/Kconfig b/drivers/devfreq/Kconfig
>> index 38a94df749a2..c799917c34c9 100644
>> --- a/drivers/devfreq/Kconfig
>> +++ b/drivers/devfreq/Kconfig
>> @@ -74,6 +74,18 @@ config DEVFREQ_GOV_PASSIVE
>>  	  through sysfs entries. The passive governor recommends that
>>  	  devfreq device uses the OPP table to get the frequency/voltage.
>>  
>> +comment "DEVFREQ Options"
>> +
>> +config DEVFREQ_DELAYED_TIMER
>> +	bool "Use delayed timer in Simple Ondemand Governor"
> 
> Is the use really limited to the Simple Ondemand Governor? I don't think
> so, at least the Tegra devfreq driver also does monitoring and others
> might follow.

There are currently:

simple_ondemand
performance
powersave
userspace
passive

From them perfomance, powersave and userspace are fixed max, min or user provided,
so only left simple_ondemand and passive which could benefit from change.

>> +	default false
>> +	help
>> +	  Simple Ondemand Governor uses polling for reading buses counters.
>> +	  A default timer used is deferred, which saves power, but can
>> +	  miss increased demand for higher bus frequency if timer was
>> +	  assigned to idle cpu. If you want to change this to delayed
>> +	  timer at the cost of more power used, say Yes here.
>> +
>>  comment "DEVFREQ Drivers"
>>  
>>  config ARM_EXYNOS_BUS_DEVFREQ
> 
> 
> This patch on it's own does nothing. Squash it with '[4/4] PM / devfreq:
> use delayed work if DEVFREQ_DELAYED_TIMER set'.
> 
> 

-- 
Best regards,
Kamil Konieczny
Samsung R&D Institute Poland

Re: [PATCH 1/4] PM / devfreq: reuse system workqueue machanism

[Chanwoo Choi]

On 12/10/19 6:28 PM, Kamil Konieczny wrote:
> Hi Chanwoo,
> 
> On 10.12.2019 08:53, Chanwoo Choi wrote:
>> On 12/10/19 4:28 PM, Kamil Konieczny wrote:
>>> On 10.12.2019 02:41, Chanwoo Choi wrote:
>>>> On 12/9/19 11:44 PM, Kamil Konieczny wrote:
>>>>> There is no need for creating another workqueue, it is enough
>>>>> to reuse system_freezable_power_efficient one.
>>>>>
>>>>> Signed-off-by: Kamil Konieczny <k.konieczny@samsung.com>
>>>>> ---
>>>>>  drivers/devfreq/devfreq.c | 6 +++---
>>>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>
>>>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>>>> index 46a7ff7c2994..955949c6fc1f 100644
>>>>> --- a/drivers/devfreq/devfreq.c
>>>>> +++ b/drivers/devfreq/devfreq.c
>>>>> @@ -1532,11 +1532,11 @@ static int __init devfreq_init(void)
>>>>>  		return PTR_ERR(devfreq_class);
>>>>>  	}
>>>>>  
>>>>> -	devfreq_wq = create_freezable_workqueue("devfreq_wq");
>>>>> +	devfreq_wq = system_freezable_power_efficient_wq;
>>>>
>>>> It affect the behaviors of whole device drivers using devfreq subsystem.
>>>> It is not good to change the workqueue type without any reasonable
>>>> data like experiment result, power-consumption result and performance
>>>> result for almost device drivers using devfreq subsystem.
>>>>
>>>> Are there any problem or any benefit to change workqueue type?
>>>
>>> The workqueue is freezable with additional capability of 'power_efficient',
>>> it is already developed by linux community so why not reuse it ?
>>
>> As you agreed below, why don't you suggest the any reasonable test result
>> with this patch? As I commented, it affects the all device drivers. 
>> It is necessary to suggest the test result on multiple scenarios
>> in order to prevent the any power-consumption and performance regression.
>> It is not easy to change them without any data.
>>
>> Frankly, if you test almost scenarios and suggest the reasonable result
>> that anyone can understand, like there are never difference
>> between "create_freezable_workqueue("devfreq_wq");" and system_freezable_power_efficient_wq.
>> But you don't suggest any data.
> 
> I agree about tests data needed for deciding about change. As I already wrote in other
> letter, I do not have such tests procedures, so if you have them and you may share
> them with me or Marek, I can run them and gather tests results.
> 
>> - The original devfreq_wq include the only work related to devfreq.
>> - system_freezable_power_efficient_wq include the all works registered
>> from both other subsystem and device drivers in linux kernel.
> 
> I do not know that good system wq, devfreq_wq have only one work item so
> imho it is not beneficial to use separate wq. Seperate wq can be good
> during debugging problems with wq.

No, devfreq_wq has not ony one work item. If one target use the multiple
devfreq device with simple_ondemand governor, devfreq_wq has the 
the multiple work item. It depends on the number of devfreq device
with simple_ondemand governor.

> 
>>>> Actually, it is not simple to change the like just one device driver
>>>> because devfreq subsytem is very important for both performance
>>>> and power-consumption.
>>>
>>> I agree. The name of this wq promises what you want, both freezable
>>> and power efficiency.
>>>
>>>> If you hope to change the feature related to both performance 
>>>> and power-consumption, please suggest the reasonable data
>>>> with fundamental reason.
>>>>
>>>> So, I can't agree it.
>>>>
>>>>
>>>>>  	if (!devfreq_wq) {
>>>>>  		class_destroy(devfreq_class);
>>>>> -		pr_err("%s: couldn't create workqueue\n", __FILE__);
>>>>> -		return -ENOMEM;
>>>>> +		pr_err("%s: system_freezable_power_efficient_wq isn't initialized\n", __FILE__);
>>>>> +		return -EINVAL;
>>>>>  	}
>>>>>  	devfreq_class->dev_groups = devfreq_groups;
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics

Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

[Kamil Konieczny]

Hi,

On 09.12.2019 20:27, Matthias Kaehlcke wrote:
> Hi,
> 
> On Mon, Dec 09, 2019 at 03:44:23PM +0100, 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.
>>
>> 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;
> 
> devfreq is zero initialized (allocated with kzalloc()), hence this is
> unnecessary.

ok, I will remove it

> 
>>  
>>  	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);
> 
> get rid of 'i' and just use df->delayed_timer in sprintf().

ok

> 
>> +}
>> +
>> +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;
> 
> Not a great name, the variable doesn't hold a timer. I'd suggest something
> like 'prev_val'.

ok, will change to 'bool prev, value;'

> 
>> +	int value, ret;
>> +
>> +	if (!df->governor)
>> +		return -EINVAL;
>> +
>> +	ret = kstrtoint(buf, 10, &value);
>> +	if (ret || (value != 1 && value != 0))
>> +		return -EINVAL;
> 
> use kstrtobool() instead of partially re-implementing it.

ok

>> +
>> +	mutex_lock(&df->lock);
>> +	old_timer = df->delayed_timer;
>> +	df->delayed_timer = value == 0 ? false : true;
> 
> What's wrong with:
> 
> df->delayed_timer = value;
> 
> ?

ok, when I change type of value and use above kstrtobool, this will be ok

> 
>> +	mutex_unlock(&df->lock);
> 
> Does the locking as is actually provide any value? The use case seems to
> be concurrent setting of the sysfs attribute. The lock is released after
> the assignment, hence the value of 'df->delayed_timer' could be overwritten
> before the condition below is evaluated.

Good point, before send I spotted these lines and "optimized" code so it got worse...

> If you want to protect against this case you need something like this:
> 
> // don't release the lock before evaluating the condition
> 
>> +	if (old_timer != df->delayed_timer) {

even better: if (prev != value) {
so no need for ugly mutex_unlock in both if-else paths

>   	   	mutex_unlock(&df->lock);

>> +		devfreq_monitor_stop(df);
>> +		devfreq_monitor_start(df);
>> +	}
>   	else {
> 		mutex_unlock(&df->lock);
> 	}
> 
> I don't pretend it's pretty ;-)

Thank you for review.

-- 
Best regards,
Kamil Konieczny
Samsung R&D Institute Poland

Re: [PATCH 2/4] PM / devfreq: add possibility for delayed work

[Kamil Konieczny]

Hi Chanwoo,

here are some logs from Exynos XU3 with next-20200113
As you can see from them, counters saturate to -1 and then are useless.
The solution will be to change workqueue type from DEFERRED into DELAYED
(default polling time 50ms or few times more seems fine).

I changed exynos-nocp for some more debug data:

--- a/drivers/devfreq/event/exynos-nocp.c
+++ b/drivers/devfreq/event/exynos-nocp.c
@@ -167,7 +167,8 @@ static int exynos_nocp_get_event(struct devfreq_event_dev *edev,
        edata->load_count = ((counter[1] << 16) | counter[0]);
        edata->total_count = ((counter[3] << 16) | counter[2]);
 
-       dev_dbg(&edev->dev, "%s (event: %ld/%ld)\n", edev->desc->name,
+       dev_dbg(&edev->dev, "%s (event: %ld/%ld) %08lx/%08lx\n", edev->desc->name,
+edata->load_count, edata->total_count,
 edata->load_count, edata->total_count);

Below are logs:

root@target:~/devfreq# cat nocp_debug
echo -n 'func exynos_nocp_get_event +p' > /sys/kernel/debug/dynamic_debug/control

root@target:~/devfreq# dmesg|tail
[  171.619022] devfreq-event event2: nocp@10ca1800 (event: 15170920/4932961) 00e77d68/004b4561
[  171.619088] devfreq-event event3: nocp@10ca1c00 (event: 0/4931345) 00000000/004b3f11
[  194.358276] devfreq-event event0: nocp@10ca1000 (event: -1/1875960257) ffffffff/6fd0e1c1
[  194.358529] devfreq-event event1: nocp@10ca1400 (event: 0/1875978297) 00000000/6fd12839
[  194.358860] devfreq-event event2: nocp@10ca1800 (event: -1/1875994997) ffffffff/6fd16975
[  194.359162] devfreq-event event3: nocp@10ca1c00 (event: 0/1876014197) 00000000/6fd1b475
[  194.457796] devfreq-event event0: nocp@10ca1000 (event: 25127060/8085549) 017f6894/007b602d
[  194.457930] devfreq-event event1: nocp@10ca1400 (event: 0/8062505) 00000000/007b0629
[  194.458044] devfreq-event event2: nocp@10ca1800 (event: 24674808/8032785) 017881f8/007a9211
[  194.458160] devfreq-event event3: nocp@10ca1c00 (event: 0/8014513) 00000000/007a4ab1

root@target:~/devfreq# dmesg|tail                                                                                             
[  938.626509] devfreq-event event2: nocp@10ca1800 (event: -1/-1) ffffffff/ffffffff                                           
[  938.626656] devfreq-event event3: nocp@10ca1c00 (event: 0/-1) 00000000/ffffffff                                            
[ 1026.756029] devfreq-event event0: nocp@10ca1000 (event: -1/-1) ffffffff/ffffffff                                           
[ 1026.756386] devfreq-event event1: nocp@10ca1400 (event: 0/-1) 00000000/ffffffff                                            
[ 1026.756620] devfreq-event event2: nocp@10ca1800 (event: -1/-1) ffffffff/ffffffff                                           
[ 1026.756831] devfreq-event event3: nocp@10ca1c00 (event: 0/-1) 00000000/ffffffff                                            
[ 1026.875345] devfreq-event event0: nocp@10ca1000 (event: 30306432/9742217) 01ce7080/0094a789                                
[ 1026.875466] devfreq-event event1: nocp@10ca1400 (event: 0/9733001) 00000000/00948389                                       
[ 1026.875562] devfreq-event event2: nocp@10ca1800 (event: 29891212/9717537) 01c81a8c/00944721                                
[ 1026.875658] devfreq-event event3: nocp@10ca1c00 (event: 0/9702245) 00000000/00940b65                                       
root@target:~/devfreq# dmesg|tail                                                                                             
[ 1231.215227] devfreq-event event2: nocp@10ca1800 (event: 20069796/6510789) 01323da4/006358c5                                
[ 1231.215362] devfreq-event event3: nocp@10ca1c00 (event: 0/6505265) 00000000/00634331                                       
[ 1231.274744] devfreq-event event0: nocp@10ca1000 (event: 15373176/4877213) 00ea9378/004a6b9d                                
[ 1231.274840] devfreq-event event1: nocp@10ca1400 (event: 0/4869301) 00000000/004a4cb5                                       
[ 1231.274928] devfreq-event event2: nocp@10ca1800 (event: 15107524/4860117) 00e685c4/004a28d5                                
[ 1231.275017] devfreq-event event3: nocp@10ca1c00 (event: 0/4850901) 00000000/004a04d5                                       
[ 1345.925227] devfreq-event event0: nocp@10ca1000 (event: -1/-1) ffffffff/ffffffff                                           
[ 1345.925540] devfreq-event event1: nocp@10ca1400 (event: 0/-1) 00000000/ffffffff                                            
[ 1345.925751] devfreq-event event2: nocp@10ca1800 (event: -1/-1) ffffffff/ffffffff                                           
[ 1345.926095] devfreq-event event3: nocp@10ca1c00 (event: 0/-1) 00000000/ffffffff                                            
root@target:~/devfreq# uname -a                                                                                               
Linux target 5.5.0-rc5-next-20200113-00001-g9c27c4bdca7e #82 SMP PREEMPT Mon Jan 20 14:31:11 CET 2020 armv7l GNU/Linux        
root@target:~/devfreq# cat /sys/class/devfreq/devfreq2/trans_stat                                                             
     From  :   To                                                                                                             
           :  88700000 133000000 177400000 266000000 532000000   time(ms)                                                     
*  88700000:         0         0         0         0        31    660390                                                      
  133000000:         4         0         0         0         3     32630                                                      
  177400000:         2         0         0         0         1    103520                                                      
  266000000:         1         2         1         0         0      8020                                                      
  532000000:        24         5         2         4         0    680050                                                      
Total transition : 80

On 10.12.2019 10:03, 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 ?
> 
>> 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
> 
>> 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.
> 
>>>
>>> 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,
Kamil Konieczny
Samsung R&D Institute Poland