Re: [RFC PATCH 1/7] PM: Introduce em_pd_get_higher_freq()

[Douglas Raillard]

Hi Patrick,

On 5/16/19 2:22 PM, Patrick Bellasi wrote:
> On 16-May 14:01, Quentin Perret wrote:
> > On Thursday 16 May 2019 at 13:42:00 (+0100), Patrick Bellasi wrote:
> > > > +static inline unsigned long em_pd_get_higher_freq(struct em_perf_domain *pd,
> > > > +	unsigned long min_freq, unsigned long cost_margin)
> > > > +{
> > > > +	unsigned long max_cost = 0;
> > > > +	struct em_cap_state *cs;
> > > > +	int i;
> > > > +
> > > > +	if (!pd)
> > > > +		return min_freq;
> > > > +
> > > > +	/* Compute the maximum allowed cost */
> > > > +	for (i = 0; i < pd->nr_cap_states; i++) {
> > > > +		cs = &pd->table[i];
> > > > +		if (cs->frequency >= min_freq) {
> > > > +			max_cost = cs->cost + (cs->cost * cost_margin) / 1024;
> > >                                                                           ^^^^
> > > ... end here we should probably better use SCHED_CAPACITY_SCALE
> > > instead of hard-coding in values, isn't it?
> >
> > I'm not sure to agree. This isn't part of the scheduler per se, and the
> > cost thing isn't in units of capacity, but in units of power, so I don't
> > think SCHED_CAPACITY_SCALE is correct here.
>
> Right, I get the units do not match and it would not be elegant to use
> it here...
>
> > But I agree these hard coded values (that one, and the 512 in one of the
> > following patches) could use some motivation :-)
>
> ... ultimately SCHED_CAPACITY_SCALE is just SCHED_FIXEDPOINT_SCALE,
> which is adimensional. Perhaps we should use that or yet another alias
> for the same.

Would it be a good idea to use SCHED_FIXEDPOINT_SCALE in energy.c ?
Since it's not part of the scheduler, maybe there is a scale covering a wider scope,
or we can introduce a similar ENERGY_FIXEDPOINT_SCALE in energy_model.h.


> > Thanks,
> > Quentin

Thanks,
Douglas