Re: [PATCH v7 02/14] sched/cpufreq: Prepare schedutil for Energy Aware Scheduling

Rafael J. Wysocki
2018-09-28T08:23:42Z

On Thursday, September 27, 2018 2:17:49 PM CEST Quentin Perret wrote:
> Hi Rafael,
>
> Very sorry for the late reply ...
>
> On Tuesday 18 Sep 2018 at 23:33:22 (+0200), Rafael J. Wysocki wrote:
> [...]
> > The new "type" argument should be documented.
> >
> > Also IMO using the special enum for it is quite confusing, because you
> > ever only check one value from it directly. What would be wrong with
> > using a plain "bool" instead?
>
> So, this part of the code was originally proposed by Peter. I basically
> took it from the following message (hence the Suggested-by) which was
> fine by me:
>
> https://lore.kernel.org/lkml/20180709120138.GQ2494@hirez.programming.kicks-ass.net/
>
> Also, one of the things that has been mentioned during reviews was that
> other clients (such as cpuidle, IIRC) could potentially be interested
> in a 'global' cpu util value. And since those clients might have
> different needs than EAS or sugov, they might need a new entry in the
> enum.
>
> So that's probably the main argument for the enum, it is easy to extend.

OK, so please document the enum type.

> [...]
> > > +static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
> > > +{
> > > + struct rq *rq = cpu_rq(sg_cpu->cpu);
> > > + unsigned long util = cpu_util_cfs(rq);
> > > +
> > > + sg_cpu->max = arch_scale_cpu_capacity(NULL, sg_cpu->cpu);
> > > + sg_cpu->bw_dl = cpu_bw_dl(rq);
> > > +
> > > + return schedutil_freq_util(sg_cpu->cpu, util, FREQUENCY_UTIL);
> >
> > If you add a "max" argument to schedutil_freq_util(), you can avoid
> > the second (and arguably redundant) evaluation of
> > arch_scale_cpu_capacity() in there.
>
> OK
>
> [...]
> > > +enum schedutil_type {
> > > + FREQUENCY_UTIL,
> > > + ENERGY_UTIL,
> > > +};
> >
> > As I said above, I would just use "bool" instead of this new enum (it
> > has two values too) or the new type needs to be documented.
>
> As I said above, the enum has the good side of being easier to extend.
> So, if we care about that, I guess I'd rather add a doc for the new
> type.

Right, so please add a kerneldoc description here.

> > > +
> > > #ifdef CONFIG_CPU_FREQ_GOV_SCHEDUTIL
> > > +unsigned long schedutil_freq_util(int cpu, unsigned long util_cfs,
> > > + enum schedutil_type type);
> > > +
> > > static inline unsigned long cpu_bw_dl(struct rq *rq)
> > > {
> > > return (rq->dl.running_bw * SCHED_CAPACITY_SCALE) >> BW_SHIFT;
> > > @@ -2199,6 +2207,12 @@ static inline unsigned long cpu_util_rt(struct rq *rq)
> > > {
> > > return READ_ONCE(rq->avg_rt.util_avg);
> > > }
> > > +#else /* CONFIG_CPU_FREQ_GOV_SCHEDUTIL */
> > > +static inline unsigned long schedutil_freq_util(int cpu, unsigned long util,
> > > + enum schedutil_type type)
> > > +{
> > > + return util;
> > > +}
> > > #endif
> >
> > And I would add a wrapper around schedutil_freq_util(), called say
> > schedutil_energy_util(), that would pass a specific value as the
> > "type".
>
> OK, that's fine by me.
>
> Other than that, do you think these changes could be done later ? Or do
> you see that as mandatory before the patches can be picked up ?

Documenting things properly is absolutely required.

The other changes suggested by me are rather straightforward, so why would it
be a problem to make them right away if you agree to make them?

Thanks,
Rafael