Re: [PATCH v6 04/10] PM / EM: add support for other devices than CPUs in Energy Model

[Lukasz Luba]

On 4/10/20 12:12 PM, Luis Gerhorst wrote:
> Lukasz Luba writes:
>
> > +/**
> > + * em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for 
> > a device
> > + * @devÂÂÂÂÂÂÂ : Device for which the EM is registered
> > + *
> > + * Try to unregister the EM for the specified device (it checks current
> > + * reference counter). The EM for CPUs will not be freed.
> > + */
> > +void em_dev_unregister_perf_domain(struct device *dev)
> > +{
> > +ÂÂÂ struct em_device *em_dev, *tmp;
> > +
> > +ÂÂÂ if (IS_ERR_OR_NULL(dev))
> > +ÂÂÂÂÂÂÂ return;
> > +
> > +ÂÂÂ /* We don't support freeing CPU structures in hotplug */
> > +ÂÂÂ if (_is_cpu_device(dev)) {
> > +ÂÂÂÂÂÂÂ dev_dbg_once(dev, "EM: the structures are not going to be 
> > removed\n");
> > +ÂÂÂÂÂÂÂ return;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ mutex_lock(&em_pd_mutex);
> > +
> > +ÂÂÂ if (list_empty(&em_pd_dev_list)) {
> > +ÂÂÂÂÂÂÂ mutex_unlock(&em_pd_mutex);
> > +ÂÂÂÂÂÂÂ return;
> > +ÂÂÂ }
> > +
> > +ÂÂÂ list_for_each_entry_safe(em_dev, tmp, &em_pd_dev_list, 
> > em_dev_list) {
> > +ÂÂÂÂÂÂÂ if (em_dev->dev == dev) {
> > +ÂÂÂÂÂÂÂÂÂÂÂ kref_put(&em_dev->kref, _em_release);
> > +ÂÂÂÂÂÂÂÂÂÂÂ break;
> > +ÂÂÂÂÂÂÂ }
> > +ÂÂÂ }
> > +
> > +ÂÂÂ mutex_unlock(&em_pd_mutex);
> > +}
> > +EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);
>
> Ok, so em_dev_unregister_perf_domain() does not support the CPU device
> and a subsequent em_register_perf_domain() will fail with EEXIST.

Correct. At the current mainline Energy Model we don't even have
em_unregister_perf_domain function. I had to introduce it in order
to support other devices which might have drivers loaded/unloaded
as modules.


> Is there a way to unregister/change the CPU's energy model during
> runtime without restarting the whole system?

Not for the CPU for now.

It is possible for other devices. When you have i.e. a module driver for
a device and in your code there is a (*active_power)(), then it is
possible to change EM by unloading/loading the module.

For the CPU we don't have this requirement for production code. I will
add you to CC list when something like this would pop-up for a
prototyping/experimentation code. We have been analyzing some options.

Regards,
Lukasz