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

[Lukasz Luba]

Hi Dietmar,

On 1/20/20 2:53 PM, Dietmar Eggemann wrote:
> On 16/01/2020 16:20, lukasz.luba@xxxxxxx wrote:
> > From: Lukasz Luba <lukasz.luba@xxxxxxx>
> >
> > 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

> [...]