Date:   Fri, 12 Jan 2018 09:46:08 -0800
From:   Eduardo Valentin <edubezval@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] thermal: Add cooling device's statistics in sysfs

Hello,

On Thu, Jan 11, 2018 at 03:06:09PM +0530, Viresh Kumar wrote:
> This extends the sysfs interface for thermal cooling devices and exposes
> some pretty useful statistics. These statistics have proven to be quite
> useful specially while doing benchmarks related to the task scheduler,
> where we want to make sure that nothing has disrupted the test,
> specially the cooling device which may have put constraints on the CPUs.
> The information exposed here tells us to what extent the CPUs were
> constrained by the thermal framework.
> 
> The read-only "total_trans" file shows the total number of cooling state
> transitions the device has gone through since the time the cooling
> device is registered or the time when statistics were reset last.

It would be good to properly describe what total_trans means. Also, to
have this documented in the thermal sysfs file. Does it mean how many
times the cooling device has been set to a specific state? Or how many
times the state has been changed to that specific value?

> 
> The read-only "time_in_state_ms" file shows the time spent by the device
> in the respective cooling states.

What about this file use the same unit as the cpufreq equivalent? IIRC,
the cpufreq node used clock_t.

> 
> The write-only "reset" file is used to reset the statistics.
> 

cool.

> This is how the directory structure looks like for a single cooling
> device:
> 
> $ ls -R /sys/class/thermal/cooling_device0/
> /sys/class/thermal/cooling_device0/:
> cur_state  max_state  power  stats  subsystem  type  uevent
> 
> /sys/class/thermal/cooling_device0/power:
> autosuspend_delay_ms  runtime_active_time  runtime_suspended_time
> control               runtime_status
> 
> /sys/class/thermal/cooling_device0/stats:
> reset  time_in_state_ms  total_trans
> 

I guess the only missing node from the cpufreq design copy was the
transition table.

Also, I think the stats per thermal zone is also useful, sometimes
more than per cooling device, as I have been using in
the past, but that is just a comment, not really to block your patch.

> This is tested on ARM 32-bit Hisilicon hikey620 board running Ubuntu and
> ARM 64-bit Hisilicon hikey960 board running Android.
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V2->V3:
> - Total number of states is max_level + 1. The earlier version didn't
>   take that into account and so the stats for the highest state were
>   missing.
> 
> V1->V2:
> - Move to sysfs from debugfs
> 
>  drivers/thermal/thermal_core.c    |   3 +-
>  drivers/thermal/thermal_core.h    |   3 +
>  drivers/thermal/thermal_helpers.c |   5 +-
>  drivers/thermal/thermal_sysfs.c   | 146 ++++++++++++++++++++++++++++++++++++++
>  include/linux/thermal.h           |   1 +
>  5 files changed, 156 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> index 2b1b0ba393a4..2cc4ae57484e 100644
> --- a/drivers/thermal/thermal_core.c
> +++ b/drivers/thermal/thermal_core.c
> @@ -972,8 +972,8 @@ __thermal_cooling_device_register(struct device_node *np,
>  	cdev->ops = ops;
>  	cdev->updated = false;
>  	cdev->device.class = &thermal_class;
> -	thermal_cooling_device_setup_sysfs(cdev);
>  	cdev->devdata = devdata;
> +	thermal_cooling_device_setup_sysfs(cdev);
>  	dev_set_name(&cdev->device, "cooling_device%d", cdev->id);
>  	result = device_register(&cdev->device);
>  	if (result) {
> @@ -1106,6 +1106,7 @@ void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
>  
>  	ida_simple_remove(&thermal_cdev_ida, cdev->id);
>  	device_unregister(&cdev->device);
> +	thermal_cooling_device_remove_sysfs(cdev);
>  }
>  EXPORT_SYMBOL_GPL(thermal_cooling_device_unregister);
>  
> diff --git a/drivers/thermal/thermal_core.h b/drivers/thermal/thermal_core.h
> index 27e3b1df7360..f6eb01e99816 100644
> --- a/drivers/thermal/thermal_core.h
> +++ b/drivers/thermal/thermal_core.h
> @@ -73,6 +73,9 @@ int thermal_build_list_of_policies(char *buf);
>  int thermal_zone_create_device_groups(struct thermal_zone_device *, int);
>  void thermal_zone_destroy_device_groups(struct thermal_zone_device *);
>  void thermal_cooling_device_setup_sysfs(struct thermal_cooling_device *);
> +void thermal_cooling_device_remove_sysfs(struct thermal_cooling_device *cdev);
> +void thermal_cooling_device_stats_update(struct thermal_cooling_device *cdev,
> +					 unsigned long new_state);
>  /* used only at binding time */
>  ssize_t
>  thermal_cooling_device_trip_point_show(struct device *,
> diff --git a/drivers/thermal/thermal_helpers.c b/drivers/thermal/thermal_helpers.c
> index 8cdf75adcce1..eb03d7e099bb 100644
> --- a/drivers/thermal/thermal_helpers.c
> +++ b/drivers/thermal/thermal_helpers.c
> @@ -187,7 +187,10 @@ void thermal_cdev_update(struct thermal_cooling_device *cdev)
>  		if (instance->target > target)
>  			target = instance->target;
>  	}
> -	cdev->ops->set_cur_state(cdev, target);
> +
> +	if (!cdev->ops->set_cur_state(cdev, target))
> +		thermal_cooling_device_stats_update(cdev, target);
> +

I might be wrong but, this will maybe double account for cases the same
cooling state is selected.

>  	cdev->updated = true;
>  	mutex_unlock(&cdev->lock);
>  	trace_cdev_update(cdev, target);
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index ba81c9080f6e..88bb26d5d375 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -666,6 +666,121 @@ void thermal_zone_destroy_device_groups(struct thermal_zone_device *tz)
>  }
>  
>  /* sys I/F for cooling device */
> +struct cooling_dev_stats {
> +	spinlock_t lock;
> +	unsigned int total_trans;
> +	unsigned long state;
> +	unsigned long max_states;
> +	ktime_t last_time;
> +	ktime_t *time_in_state;
> +};
> +
> +static void update_time_in_state(struct cooling_dev_stats *stats)
> +{
> +	ktime_t now = ktime_get(), delta;
> +
> +	delta = ktime_sub(now, stats->last_time);
> +	stats->time_in_state[stats->state] =
> +		ktime_add(stats->time_in_state[stats->state], delta);
> +	stats->last_time = now;
> +}
> +
> +void thermal_cooling_device_stats_update(struct thermal_cooling_device *cdev,
> +					 unsigned long new_state)
> +{
> +	struct cooling_dev_stats *stats = cdev->stats;
> +
> +	spin_lock(&stats->lock);
> +
> +	if (stats->state == new_state)
> +		goto unlock;
> +
> +	update_time_in_state(stats);
> +	stats->state = new_state;
> +	stats->total_trans++;
> +
> +unlock:
> +	spin_unlock(&stats->lock);
> +}
> +
> +static ssize_t
> +thermal_cooling_device_total_trans_show(struct device *dev,
> +					struct device_attribute *attr,
> +					char *buf)
> +{
> +	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> +	struct cooling_dev_stats *stats = cdev->stats;
> +	int ret;
> +
> +	spin_lock(&stats->lock);
> +	ret = sprintf(buf, "%u\n", stats->total_trans);
> +	spin_unlock(&stats->lock);
> +
> +	return ret;
> +}
> +
> +static ssize_t
> +thermal_cooling_device_time_in_state_show(struct device *dev,
> +					  struct device_attribute *attr,
> +					  char *buf)
> +{
> +	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> +	struct cooling_dev_stats *stats = cdev->stats;
> +	ssize_t len = 0;
> +	int i;
> +
> +	spin_lock(&stats->lock);
> +	update_time_in_state(stats);
> +
> +	for (i = 0; i < stats->max_states; i++) {
> +		len += sprintf(buf + len, "state%u\t%llu\n", i,
> +			       ktime_to_ms(stats->time_in_state[i]));
> +	}
> +	spin_unlock(&stats->lock);
> +
> +	return len;
> +}
> +
> +static ssize_t
> +thermal_cooling_device_reset_store(struct device *dev,
> +				   struct device_attribute *attr,
> +				   const char *buf, size_t count)
> +{
> +	struct thermal_cooling_device *cdev = to_cooling_device(dev);
> +	struct cooling_dev_stats *stats = cdev->stats;
> +	int i;
> +
> +	spin_lock(&stats->lock);
> +
> +	stats->total_trans = 0;
> +	stats->last_time = ktime_get();

So, this is ktime. Then again, might make sense to follow cpufreq unit.

Once again, this needs to go into the documentation, regardless of the
unit we end up with.

> +
> +	for (i = 0; i < stats->max_states; i++)
> +		stats->time_in_state[i] = ktime_set(0, 0);
> +
> +	spin_unlock(&stats->lock);
> +
> +	return count;
> +}
> +
> +static DEVICE_ATTR(total_trans, 0444, thermal_cooling_device_total_trans_show,
> +		   NULL);
> +static DEVICE_ATTR(time_in_state_ms, 0444,
> +		   thermal_cooling_device_time_in_state_show, NULL);
> +static DEVICE_ATTR(reset, 0200, NULL, thermal_cooling_device_reset_store);
> +
> +static struct attribute *cooling_device_stats_attrs[] = {
> +	&dev_attr_total_trans.attr,
> +	&dev_attr_time_in_state_ms.attr,
> +	&dev_attr_reset.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group cooling_device_stats_attr_group = {
> +	.attrs = cooling_device_stats_attrs,
> +	.name = "stats"
> +};
> +
>  static ssize_t
>  thermal_cooling_device_type_show(struct device *dev,
>  				 struct device_attribute *attr, char *buf)
> @@ -721,6 +836,7 @@ thermal_cooling_device_cur_state_store(struct device *dev,
>  	result = cdev->ops->set_cur_state(cdev, state);
>  	if (result)
>  		return result;
> +	thermal_cooling_device_stats_update(cdev, state);
>  	return count;
>  }
>  
> @@ -745,14 +861,44 @@ static const struct attribute_group cooling_device_attr_group = {
>  
>  static const struct attribute_group *cooling_device_attr_groups[] = {
>  	&cooling_device_attr_group,
> +	&cooling_device_stats_attr_group,
>  	NULL,
>  };
>  
>  void thermal_cooling_device_setup_sysfs(struct thermal_cooling_device *cdev)
>  {
> +	struct cooling_dev_stats *stats;
> +	unsigned long states;
> +	int ret, size;
> +
> +	ret = cdev->ops->get_max_state(cdev, &states);
> +	if (ret)
> +		return;
> +
> +	states++; /* Total number of states is highest state + 1 */
> +	size = sizeof(*stats);
> +	size += sizeof(*stats->time_in_state) * states;
> +
> +	stats = kzalloc(size, GFP_KERNEL);
> +	if (!stats)
> +		return;
> +
> +	stats->time_in_state = (ktime_t *)(stats + 1);
> +	cdev->stats = stats;
> +	stats->last_time = ktime_get();
> +	stats->max_states = states;
> +	cdev->stats = stats;
> +
> +	spin_lock_init(&stats->lock);

I would say, the cooling device stat initialization deserves its own
initialization function, don't you think?


Also, I see nothing about sysfs on the lines added to
thermal_cooling_device_setup_sysfs().

>  	cdev->device.groups = cooling_device_attr_groups;
>  }
>  
> +void thermal_cooling_device_remove_sysfs(struct thermal_cooling_device *cdev)
> +{
> +	kfree(cdev->stats);
> +	cdev->stats = NULL;
> +}
> +
>  /* these helper will be used only at the time of bindig */
>  ssize_t
>  thermal_cooling_device_trip_point_show(struct device *dev,
> diff --git a/include/linux/thermal.h b/include/linux/thermal.h
> index 8c5302374eaa..7834be668d80 100644
> --- a/include/linux/thermal.h
> +++ b/include/linux/thermal.h
> @@ -148,6 +148,7 @@ struct thermal_cooling_device {
>  	struct device device;
>  	struct device_node *np;
>  	void *devdata;
> +	void *stats;
>  	const struct thermal_cooling_device_ops *ops;
>  	bool updated; /* true if the cooling device does not need update */
>  	struct mutex lock; /* protect thermal_instances list */
> -- 
> 2.15.0.194.g9af6a3dea062
> 

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