Re: [PATCH v1 06/13] thermal: gov_fair_share: Rearrange get_trip_level()

Rafael J. Wysocki
2023-09-27T15:06:28Z

On Wed, Sep 27, 2023 at 5:00 PM Daniel Lezcano
<daniel.lezcano@linaro.org> wrote:
>
> On 21/09/2023 19:54, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Make get_trip_level() access the thermal zone's trip table directly
> > instead of using __thermal_zone_get_trip() which adds overhead related
> > to the unnecessary bounds checking and copying the trip point data.
> >
> > Also rearrange the code in it to make it somewhat easier to follow.
> >
> > The general functionality is not expected to be changed.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> > drivers/thermal/gov_fair_share.c | 22 ++++++++++------------
> > 1 file changed, 10 insertions(+), 12 deletions(-)
> >
> > Index: linux-pm/drivers/thermal/gov_fair_share.c
> > ===================================================================
> > --- linux-pm.orig/drivers/thermal/gov_fair_share.c
> > +++ linux-pm/drivers/thermal/gov_fair_share.c
> > @@ -21,23 +21,21 @@
> > */
> > static int get_trip_level(struct thermal_zone_device *tz)
> > {
> > - struct thermal_trip trip;
> > - int count;
> > + const struct thermal_trip *trip = tz->trips;
> > + int i;
> >
> > - for (count = 0; count < tz->num_trips; count++) {
> > - __thermal_zone_get_trip(tz, count, &trip);
> > - if (tz->temperature < trip.temperature)
> > + if (tz->temperature < trip->temperature)
> > + return 0;
> > +
> > + for (i = 0; i < tz->num_trips - 1; i++) {
> > + trip++;
> > + if (tz->temperature < trip->temperature)
> > break;
> > }
>
> Is it possible to use for_each_thermal_trip() instead ? That would make
> the code more self-encapsulate

It is possible in principle, but this is a governor which is regarded
as part of the core, isn't it?

So is an extra overhead related to using a callback (which may be
subject to retpolines and such) really justified in this case?

>
> > - /*
> > - * count > 0 only if temperature is greater than first trip
> > - * point, in which case, trip_point = count - 1
> > - */
> > - if (count > 0)
> > - trace_thermal_zone_trip(tz, count - 1, trip.type);
> > + trace_thermal_zone_trip(tz, i, tz->trips[i].type);
> >
> > - return count;
> > + return i;
> > }
> >
> > static long get_target_state(struct thermal_zone_device *tz,
> >
> >
> >
>
> --