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    SubjectRe: [RFC PATCH 1/7] PM: Introduce em_pd_get_higher_freq()
    On Friday 21 Jun 2019 at 11:17:05 (+0100), Quentin Perret wrote:
    > On Thursday 20 Jun 2019 at 14:04:39 (+0100), Patrick Bellasi wrote:
    > > On 19-Jun 17:08, Douglas Raillard wrote:
    > > > 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.
    > >
    > > Well, in energy_model.c we have references to "capacity" and
    > > "utilization" which are all SCHED_FIXEDPOINT_SCALE range values.
    > > That symbol is defined in <linux/sched.h> and we already pull
    > > in other <linux/sched/*> headers.
    > >
    > > So, to me it seems it's not unreasonable to say that we use scheduler
    > > related concepts and it makes more sense than introducing yet another
    > > scaling factor.
    > >
    > > But that's just my two cents ;)
    >
    > Perhaps use this ?
    >
    > https://elixir.bootlin.com/linux/latest/source/include/linux/energy_model.h#L43
    >

    Nah, bad idea actually ... Sorry for the noise

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