Re: [PATCH 1/4] PM / EM: and devices to Energy Model

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

Hi Dietmar,

On 1/20/20 2:53 PM, Dietmar Eggemann wrote:
> On 16/01/2020 16:20, lukasz.luba@arm.com wrote:
>> From: Lukasz Luba <lukasz.luba@arm.com>
>>
>> Add support of other devices into the Energy Model framework not only the
>> CPUs. Change the interface to be more unified which can handle other
>> devices as well.
> 
> [...]
> 
>> -The source of the information about the power consumed by CPUs can vary greatly
>> +The source of the information about the power consumed by devices can vary greatly
>>   from one platform to another. These power costs can be estimated using
>>   devicetree data in some cases. In others, the firmware will know better.
>>   Alternatively, userspace might be best positioned. And so on. In order to avoid
>> @@ -26,7 +28,7 @@ framework, and interested clients reading the data from it::
>>          | Thermal (IPA) |  | Scheduler (EAS) |  |     Other     |
>>          +---------------+  +-----------------+  +---------------+
>>                  |                   | em_pd_energy()    |
>> -               |                   | em_cpu_get()      |
>> +               |  em_dev_get()     | em_cpu_get()      |
> 
> Looked really hard but can't find a em_dev_get() in the code? You mean
> em_get_pd() ? And why em_get_pd() and not em_pd_get()?

It was it the old implementation, I will remove 'em_dev_get()' from
the doc. The em_pd_get() is OK for me, I can change it.

> 
>>                  +---------+         |         +---------+
>>                            |         |         |
>>                            v         v         v
>> @@ -47,12 +49,12 @@ framework, and interested clients reading the data from it::
>>           | Device Tree  |   |   Firmware    |  |      ?       |
>>           +--------------+   +---------------+  +--------------+
> 
> [...]
> 
>> +There is two API functions which provide the access to the energy model:
>> +em_cpu_get() which takes CPU id as an argument and em_dev_get() with device
>> +pointer as an argument. It depends on the subsystem which interface it is
>> +going to use.
> 
> Would be really nice if this wouldn't be required. We should really aim
> for 1 framework == 1 set of interfaces.
> 
> What happens if someone calls em_get_pd() on a CPU EM?
> 
> E.g:
> 
>   static struct perf_domain *pd_init(int cpu)
>   {
> -       struct em_perf_domain *obj = em_cpu_get(cpu);
> +       struct device *dev = get_cpu_device(cpu);
> +       struct em_perf_domain *obj = em_pd_get(dev);
>          struct perf_domain *pd;
> 
> Two versions of one functionality will confuse API user from the
> beginning ...

Right, I could modify the pd_init code to use one 'em_get_pd' API
and remove the 'em_cpu_get'.

> 
> [...]
> 
>> +enum em_type {
>> +	EM_SIMPLE,
>> +	EM_CPU,
>> +};
> 
> s/EM_SIMPLE/EM_DEV ?
> 
> Right now I only see energy models and _one_ specific type (the CPU EM).
> So a tag 'is a CPU EM' would suffice. No need for EM_SIMPE ...

The EM_SIMPLE is set in the em_register_perf_domain() to distinguish
CPU device which has populated 'priv' pointer and set EM_CPU.
We can just rely on 'priv == NULL' to check if we are dealing with a
CPU EM. Do you prefer this approach and get rid of em_type?

Then the code would look like:

if (em_pd->priv)
	seq_puts(s, "EM_CPU\n");
else
	seq_puts(s, "EM_SIMPLE\n");


Regards,
Lukasz

> 
> [...]
>