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

[Lukasz Luba]

On 1/20/20 3:28 PM, Quentin Perret wrote:
> On Monday 20 Jan 2020 at 15:53:35 (+0100), Dietmar Eggemann wrote:
> > 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 ...
>
> Agreed, this looks a bit confusing. It should be trivial to make
> em_dev_get() (or whatever we end up calling it) work for CPUs too,
> though. And we could always have a em_cpu_get(int cpu) API that is a
> basically a wrapper around em_dev_get() for convenience.

The problem not only here is that we have a CPU index 'int cpu'
and if we ask for device like:

struct device *dev = get_cpu_device(cpu);

It might be not the same device that was used during the
registration, when we had i.e. 4 CPUs for the same policy:

int cpu_id = cpumask_first(policy->cpus);
struct device *cpu_dev = get_cpu_device(cpu_id);
em_register_perf_domain(cpu_dev, nr_opp, &em_cb);

That's why the em_cpu_get() is different than em_get_pd(), mainly by:
if (cpumask_test_cpu(cpu, em_span_cpus(em_pd)))

It won't be simple wrapper, let me think how it could be handled
differently than it is now.

Regards,
Lukasz

> Thanks,
> Quentin