Re: [PATCH v8 4/8] PM / EM: add support for other devices than CPUs in Energy Model

[Lukasz Luba <lukasz.luba@arm.com>]

Hi Daniel,

On 6/1/20 10:44 PM, Daniel Lezcano wrote:
> On 27/05/2020 11:58, Lukasz Luba wrote:
>> Add support for other devices than CPUs. The registration function
>> does not require a valid cpumask pointer and is ready to handle new
>> devices. Some of the internal structures has been reorganized in order to
>> keep consistent view (like removing per_cpu pd pointers).
>>
>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
>> ---
> 
> [ ... ]
> 
>>   }
>>   EXPORT_SYMBOL_GPL(em_register_perf_domain);
>> +
>> +/**
>> + * em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for a device
>> + * @dev		: Device for which the EM is registered
>> + *
>> + * Try to unregister the EM for the specified device (but not a CPU).
>> + */
>> +void em_dev_unregister_perf_domain(struct device *dev)
>> +{
>> +	if (IS_ERR_OR_NULL(dev) || !dev->em_pd)
>> +		return;
>> +
>> +	if (_is_cpu_device(dev))
>> +		return;
>> +
>> +	mutex_lock(&em_pd_mutex);
> 
> Is the mutex really needed?

I just wanted to align this unregister code with register. Since there
is debugfs dir lookup and the device's EM existence checks I thought it
wouldn't harm just to lock for a while and make sure the registration
path is not used. These two paths shouldn't affect each other, but with
modules loading/unloading I wanted to play safe.
I can change it maybe to just dmb() and the end of the function if it's
a big performance problem in this unloading path. What do you think?

> 
> If this function is called that means there is no more user of the
> em_pd, no?

True, that EM users should already be unregistered i.e. thermal cooling.

> 
>> +	em_debug_remove_pd(dev);
>> +
>> +	kfree(dev->em_pd->table);
>> +	kfree(dev->em_pd);
>> +	dev->em_pd = NULL;
>> +	mutex_unlock(&em_pd_mutex);
>> +}
>> +EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);
>>
> 
> 

Thank you for reviewing this.

Regards,
Lukasz