Re: [PATCH v2 08/17] PM: EM: Introduce runtime modifiable table

[Lukasz Luba]

On 5/30/23 11:18, Dietmar Eggemann wrote:
> On 12/05/2023 11:57, Lukasz Luba wrote:
> > This patch introduces the new feature: modifiable EM perf_state table.
> > The new runtime table would be populated with a new power data to better
> > reflect the actual power. The power can vary over time e.g. due to the
> > SoC temperature change. Higher temperature can increase power values.
> > For longer running scenarios, such as game or camera, when also other
> > devices are used (e.g. GPU, ISP) the CPU power can change. The new
> > EM framework is able to addresses this issue and change the data
> > at runtime safely. The runtime modifiable EM data is used by the Energy
> > Aware Scheduler (EAS) for the task placement.
>
> It's important to say that EAS is the _only_user of the `runtime
> modifiable EM`. All the other users (thermal, etc.) are still using the
> default (basic) EM. IMHO, this fact drove the design here.

OK, I'll add that information in the header.

> > Signed-off-by: Lukasz Luba <lukasz.luba@xxxxxxx>
> > ---
> >   include/linux/energy_model.h | 13 +++++++++++++
> >   kernel/power/energy_model.c  | 24 ++++++++++++++++++++++++
> >   2 files changed, 37 insertions(+)
> >
> > diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
> > index cc2bf607191e..a616006a8130 100644
> > --- a/include/linux/energy_model.h
> > +++ b/include/linux/energy_model.h
> > @@ -36,9 +36,21 @@ struct em_perf_state {
> >    */
> >   #define EM_PERF_STATE_INEFFICIENT BIT(0)
> >   
> > +/**
> > + * struct em_perf_table - Performance states table, which can be
> > + *		runtime modifiable and protected with RCU
>
> which is `runtime modifiable` ? So `runtime modifiable performance state
> table`? RCU is obvious since we have `struct rcu_head rcu`.

Thanks, 'Runtime modifiable performance state table' sounds better.

> > + * @state:	List of performance states, in ascending order
> > + * @rcu:	RCU used for safe access and destruction
> > + */
> > +struct em_perf_table {
> > +	struct em_perf_state *state;
> > +	struct rcu_head rcu;
> > +};
> > +
> >   /**
> >    * struct em_perf_domain - Performance domain
> >    * @table:		List of performance states, in ascending order
> > + * @runtime_table:	Pointer to the runtime modified em_perf_table
>
> s/modified/modifiable
>
> [...]
>
> > @@ -237,12 +238,23 @@ static int em_create_pd(struct device *dev, int nr_states,
> >   			return -ENOMEM;
> >   	}
> >   
> > +	runtime_table = kzalloc(sizeof(*runtime_table), GFP_KERNEL);
> > +	if (!runtime_table) {
> > +		kfree(pd);
> > +		return -ENOMEM;
> > +	}
> > +
> >   	ret = em_create_perf_table(dev, pd, nr_states, cb, flags);
> >   	if (ret) {
> >   		kfree(pd);
> > +		kfree(runtime_table);
> >   		return ret;
> >   	}
> >   
> > +	/* Re-use temporally (till 1st modification) the memory */
>
> So this means that the runtime (modifiable) table
> (pd->runtime_table>state) is mapped to the default (basic) table
> (pd->default_table->state) until the first call to
> em_dev_update_perf_domain() (here mentioned as the 1st modification)?

correct

> IMHO, not easy to understand since neither the cover letter, nor
> documentation patch 15/17 describes this in a consistent story.

I'll add that to the patch header and also to the documentation patch
which is later in the series.