Re: [PATCH v2 09/17] PM: EM: Add RCU mechanism which safely cleans the old data

[Lukasz Luba]

On 5/30/23 11:02, Dietmar Eggemann wrote:
> On 12/05/2023 11:57, Lukasz Luba wrote:
> > The EM is going to support runtime modifications of the power data.
> > In order to achieve that prepare the internal mechanism. This patch
> > introduces RCU safe mechanism to clean up the old allocated EM data.
>
> s/In order to achieve that prepare the internal mechanism. This patch
> introduces/Introduce ... much shorter, same information.

OK

> [...]
>
> > +static void em_perf_runtime_table_set(struct device *dev,
> > +				      struct em_perf_table *runtime_table)
> > +{
> > +	struct em_perf_domain *pd = dev->em_pd;
> > +	struct em_perf_table *tmp;
> > +
> > +	tmp = pd->runtime_table;
> > +
> > +	rcu_assign_pointer(pd->runtime_table, runtime_table);
> > +
> > +	em_cpufreq_update_efficiencies(dev, runtime_table->state);
> > +
> > +	if (trace_em_perf_state_enabled()) {
> > +		unsigned long freq, power, cost, flags;
> > +		int i;
> > +
> > +		for (i = 0; i < pd->nr_perf_states; i++) {
> > +			freq = runtime_table->state[i].frequency;
> > +			power = runtime_table->state[i].power;
> > +			cost = runtime_table->state[i].cost;
> > +			flags = runtime_table->state[i].flags;
> > +
> > +			trace_em_perf_state(dev_name(dev), pd->nr_perf_states,
> > +					    i, freq, power, cost, flags);
> > +		}
> > +	}
> > +
> > +	/*
> > +	 * Check if the 'state' array is not actually the one from setup.
> > +	 * If it is then don't free it.
> > +	 */
> > +	if (tmp->state == pd->table)
>
> It's unfortunate that you have the refactoring in 13/17 which would lead to:
>
>   if (pd->runtime_table>state == pd->default_table->state)
>           ^^^^^^^^^^^^^              ^^^^^^^^^^^^^
>
> so people would immediately grasp one of the core concepts of the
> design: non-modifiable default_table and modifiable runtime_table.
>
> I still belief that it would be the better idea to do the refactoring first.
>
> [...]

That make sense. Let me try that approach as see how the patch set would
look like.