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Date: Mon, 18 Jan 2021 18:26:11 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Greg KH <greg@...ah.com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
cw00.choi@...sung.com, myungjoo.ham@...sung.com,
kyungmin.park@...sung.com
Subject: Re: [PATCH] PM / devfreq: Add sysfs attributes to simple_ondemand
governor
On 1/18/21 6:14 PM, Greg KH wrote:
> On Mon, Jan 18, 2021 at 05:56:06PM +0000, Lukasz Luba wrote:
>>
>>
>> On 1/18/21 5:17 PM, Greg KH wrote:
>>> On Fri, Jan 15, 2021 at 05:05:30PM +0000, Lukasz Luba wrote:
>>>> The simple_ondemand devfreq governor is used by quite a few devices, like
>>>> GPUs, DSPs, memory controllers, etc. It implements algorithm which tries
>>>> to predict the device frequency based on past statistics. There are two
>>>> tunables for the algorithm: 'upthreshold' and 'downdifferential'. These
>>>> tunables change the behavior of the decision, e.g. how fast to increase
>>>> the frequency or how rapidly limit the frequency. These values might be
>>>> different based on the application which is currently running, e.g.
>>>> different behavior is needed for a game than for web browsing or clean
>>>> desktop. The patch exports these two tunables so they can be adjusted
>>>> based on current need. There is also a check with the allowed ranges
>>>> to make sure the values are correct and safe.
>>>>
>>>> Signed-off-by: Lukasz Luba <lukasz.luba@....com>
>>>> ---
>>>> drivers/devfreq/governor_simpleondemand.c | 135 ++++++++++++++++++++++
>>>> 1 file changed, 135 insertions(+)
>>>>
>>>> diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
>>>> index d57b82a2b570..4b3c182e0a49 100644
>>>> --- a/drivers/devfreq/governor_simpleondemand.c
>>>> +++ b/drivers/devfreq/governor_simpleondemand.c
>>>> @@ -15,6 +15,7 @@
>>>> /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
>>>> #define DFSO_UPTHRESHOLD (90)
>>>> #define DFSO_DOWNDIFFERENCTIAL (5)
>>>> +#define DFSO_MAX_VALUE (100)
>>>> static int devfreq_simple_ondemand_func(struct devfreq *df,
>>>> unsigned long *freq)
>>>> {
>>>> @@ -84,15 +85,149 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
>>>> return 0;
>>>> }
>>>> +static ssize_t upthreshold_show(struct device *dev,
>>>> + struct device_attribute *attr, char *buf)
>>>> +{
>>>> + struct devfreq_simple_ondemand_data *data;
>>>> + struct devfreq *df = to_devfreq(dev);
>>>> +
>>>> + if (!df->data)
>>>> + return -EINVAL;
>>>> +
>>>> + data = df->data;
>>>> +
>>>> + return sprintf(buf, "%d\n", data->upthreshold);
>>>
>>> sysfs_emit()?
>>>
>>> Also, you forgot the Documentation/ABI/ updates for new sysfs files :(
>>
>> True, I will remember next time.
>>
>>>
>>>
>>>> +}
>>>> +
>>>> +static ssize_t upthreshold_store(struct device *dev,
>>>> + struct device_attribute *attr,
>>>> + const char *buf, size_t count)
>>>> +{
>>>> + struct devfreq_simple_ondemand_data *data;
>>>> + struct devfreq *df = to_devfreq(dev);
>>>> + unsigned int value;
>>>> + int ret;
>>>> +
>>>> + if (!df->data)
>>>> + return -EINVAL;
>>>> +
>>>> + data = df->data;
>>>> +
>>>> + ret = kstrtouint(buf, 10, &value);
>>>> + if (ret < 0)
>>>> + return -EINVAL;
>>>> +
>>>> + mutex_lock(&df->lock);
>>>> +
>>>> + if (value > DFSO_MAX_VALUE || value <= data->downdifferential) {
>>>> + mutex_unlock(&df->lock);
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + data->upthreshold = value;
>>>> + mutex_unlock(&df->lock);
>>>> +
>>>> + return count;
>>>> +}
>>>> +static DEVICE_ATTR_RW(upthreshold);
>>>> +
>>>> +static ssize_t downdifferential_show(struct device *dev,
>>>> + struct device_attribute *attr, char *buf)
>>>> +{
>>>> + struct devfreq_simple_ondemand_data *data;
>>>> + struct devfreq *df = to_devfreq(dev);
>>>> +
>>>> + if (!df->data)
>>>> + return -EINVAL;
>>>> +
>>>> + data = df->data;
>>>> +
>>>> + return sprintf(buf, "%d\n", data->downdifferential);
>>>> +}
>>>> +
>>>> +static ssize_t downdifferential_store(struct device *dev,
>>>> + struct device_attribute *attr,
>>>> + const char *buf, size_t count)
>>>> +{
>>>> + struct devfreq_simple_ondemand_data *data;
>>>> + struct devfreq *df = to_devfreq(dev);
>>>> + unsigned int value;
>>>> + int ret;
>>>> +
>>>> + if (!df->data)
>>>> + return -EINVAL;
>>>> +
>>>> + data = df->data;
>>>> +
>>>> + ret = kstrtouint(buf, 10, &value);
>>>> + if (ret < 0)
>>>> + return -EINVAL;
>>>> +
>>>> + mutex_lock(&df->lock);
>>>> +
>>>> + if (value > DFSO_MAX_VALUE || value >= data->upthreshold) {
>>>> + mutex_unlock(&df->lock);
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + data->downdifferential = value;
>>>> + mutex_unlock(&df->lock);
>>>> +
>>>> + return count;
>>>> +}
>>>> +static DEVICE_ATTR_RW(downdifferential);
>>>> +
>>>> +static void devfreq_simple_ondemand_sysfs_setup(struct devfreq *df)
>>>> +{
>>>> + struct devfreq_simple_ondemand_data *data;
>>>> + int ret;
>>>> +
>>>> + if (!df->data) {
>>>> + /* The memory will be freed automatically */
>>>> + df->data = devm_kzalloc(&df->dev,
>>>> + sizeof(struct devfreq_simple_ondemand_data),
>>>> + GFP_KERNEL);
>>>> + if (!df->data) {
>>>> + dev_warn(&df->dev, "Unable to allocate memory");
>>>> + return;
>>>> + }
>>>> + }
>>>> +
>>>> + data = df->data;
>>>> +
>>>> + /* After new allocation setup default values, since they are used */
>>>> + if (!data->upthreshold)
>>>> + data->upthreshold = DFSO_UPTHRESHOLD;
>>>> +
>>>> + if (!data->downdifferential)
>>>> + data->downdifferential = DFSO_DOWNDIFFERENCTIAL;
>>>> +
>>>> + ret = sysfs_create_file(&df->dev.kobj, &dev_attr_upthreshold.attr);
>>>> + if (ret < 0)
>>>> + dev_warn(&df->dev, "Unable to create 'upthreshold' attr\n");
>>>> +
>>>> + ret = sysfs_create_file(&df->dev.kobj, &dev_attr_downdifferential.attr);
>>>> + if (ret < 0)
>>>> + dev_warn(&df->dev, "Unable to create 'downdifferential' attr\n");
>>>
>>> You just raced with userspace and lost :(
>>>
>>> Please use the default sysfs groups so that it all works properly.
>>>
>>> Huge hint, when calling sysfs_* from a driver, that usually means you
>>> are doing something wrong.
>>
>> I should have used kobject_init_and_add() and the default devfreq
>> sysfs group as a parent.
>
> No, never use "raw" kobjects in the sys/devices/ tree, that is a sure
> way to ensure that userspace will never be notified or see your
> attributes.
Interesting, I've seen it in the schedutil governor, but might in a
different context.
Regards,
Lukasz
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