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

[Lukasz Luba]

On 1/21/20 10:08 AM, Quentin Perret wrote:
> On Monday 20 Jan 2020 at 16:20:49 (+0000), Lukasz Luba wrote:
> > On 1/20/20 3:28 PM, Quentin Perret wrote:
> > > 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.
>
> Right so I suppose the easiest solution would be to do the opposite of
> my first suggestion. That is, make em_get_pd() call em_cpu_get() if the
> device is a CPU device, or proceed to the PD list iteration for other
> devices. And em_cpu_get() can remain as you originally suggested (that
> is, iterate over the PDs and test the mask).

Exactly, something like:
---------------------------->8-------------------------
288 struct em_perf_domain *em_get_pd(struct device *dev)
289 {
290         struct em_device *em_dev;
291
292         if (IS_ERR_OR_NULL(dev))
293                 return NULL;
294
295         if (_is_cpu_device(dev))
296                 return em_cpu_get(dev->id);
....
------------------------8<-----------------------------

> That should ensure em_get_pd() always works, em_cpu_get() is still there
> handy for the scheduler and such, and the two EM lookup functions (for
> CPUs or for devices) are kept cleanly separated.
>
> Thoughts ?

Agree. Then we can have these two functions and em_get_pd() will also
work fine.

> Thanks,
> Quentin

Regards,
Lukasz