Re: [PATCH 2/7] sched/uclamp: Make task_fits_capacity() use util_fits_cpu()

[Vincent Guittot <vincent.guittot@linaro.org>]

On Wed, 27 Jul 2022 at 18:05, Qais Yousef <qais.yousef@arm.com> wrote:
>
> Hi Vincent
>
> On 07/22/22 10:19, Vincent Guittot wrote:
> > Le jeudi 21 juil. 2022 � 15:29:49 (+0100), Qais Yousef a �crit :
> > > On 07/12/22 11:48, Qais Yousef wrote:
> > > > On 07/11/22 15:09, Vincent Guittot wrote:
> > > > > On Wed, 29 Jun 2022 at 21:48, Qais Yousef <qais.yousef@arm.com> wrote:
> > > >
> >
> > [...]
> >
> > > > > > @@ -9108,7 +9125,7 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
> > > > > >
> > > > > >         /* Check if task fits in the group */
> > > > > >         if (sd->flags & SD_ASYM_CPUCAPACITY &&
> > > > > > -           !task_fits_capacity(p, group->sgc->max_capacity)) {
> > > > > > +           !task_fits_cpu(p, group->sgc->max_capacity_cpu)) {
> > > > >
> > > > > All the changes and added complexity above for this line. Can't you
> > > > > find another way ?
> > > >
> > > > You're right, I might have got carried away trying to keep the logic the same.
> > > >
> > > > Can we use group->asym_prefer_cpu or pick a cpu from group->sgc->cpumask
> > > > instead?
> > > >
> > > > I'll dig more into it anyway and try to come up with simpler alternative.
> > >
> > > Actually we can't.
> > >
> > > I can keep the current {max,min}_capacity field and just add the new
> > > {max,min}_capacity_cpu and use them where needed. Should address your concerns
> > > this way? That was actually the first version of the code, but then it seemed
> > > redundant to keep both {max,min}_capacity and {max,min}_capacity_cpu.
> > >
> > > OR
> > >
> > > I can add a new function to search for max spare capacity cpu in the group.
> > >
> > > Preference?
> > >
> >
> > Isn't the below enough and much simpler ?
>
> Thanks for that!
>
> >
> > [PATCH] sched/uclamp: Make task_fits_capacity() use util_fits_cpu()
> >
> > So that the new uclamp rules in regard to migration margin and capacity
> > pressure are taken into account correctly.
> > ---
> >  kernel/sched/fair.c  | 25 +++++++++++++++----------
> >  kernel/sched/sched.h |  9 +++++++++
> >  2 files changed, 24 insertions(+), 10 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 5eecae32a0f6..3e0c7cc490be 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4317,10 +4317,12 @@ static inline int util_fits_cpu(unsigned long util,
> >       return fits;
> >  }
> >
> > -static inline int task_fits_capacity(struct task_struct *p,
> > -                                  unsigned long capacity)
> > +static inline int task_fits_cpu(struct task_struct *p, int cpu)
> >  {
> > -     return fits_capacity(uclamp_task_util(p), capacity);
> > +     unsigned long uclamp_min = uclamp_eff_value(p, UCLAMP_MIN);
> > +     unsigned long uclamp_max = uclamp_eff_value(p, UCLAMP_MAX);
> > +     unsigned long util = task_util_est(p);
> > +     return util_fits_cpu(util, uclamp_min, uclamp_max, cpu);
> >  }
> >
> >  static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
> > @@ -4333,7 +4335,7 @@ static inline void update_misfit_status(struct task_struct *p, struct rq *rq)
> >               return;
> >       }
> >
> > -     if (task_fits_capacity(p, capacity_of(cpu_of(rq)))) {
> > +     if (task_fits_cpu(p, cpu_of(rq))) {
> >               rq->misfit_task_load = 0;
> >               return;
> >       }
> > @@ -8104,7 +8106,7 @@ static int detach_tasks(struct lb_env *env)
> >
> >               case migrate_misfit:
> >                       /* This is not a misfit task */
> > -                     if (task_fits_capacity(p, capacity_of(env->src_cpu)))
> > +                     if (task_fits_cpu(p, env->src_cpu))
> >                               goto next;
> >
> >                       env->imbalance = 0;
> > @@ -9085,6 +9087,10 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
> >
> >       memset(sgs, 0, sizeof(*sgs));
> >
> > +     /* Assume that task can't fit any CPU of the group */
> > +     if (sd->flags & SD_ASYM_CPUCAPACITY)
> > +             sgs->group_misfit_task_load = 0;
>
> Should this be
>
>         sgs->group_misfit_task_load = 1
>
> to indicate it doesn't fit?

Yes

>
> > +
> >       for_each_cpu(i, sched_group_span(group)) {
> >               struct rq *rq = cpu_rq(i);
> >               unsigned int local;
> > @@ -9104,12 +9110,11 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
> >               if (!nr_running && idle_cpu_without(i, p))
> >                       sgs->idle_cpus++;
> >
> > -     }
> > +             /* Check if task fits in the CPU */
> > +             if (sd->flags & SD_ASYM_CPUCAPACITY &&
> > +                 task_fits_cpu(p, i))
> > +                     sgs->group_misfit_task_load = 0;
>
> So we clear the flag if there's any cpu that fits, I think that should work,
> yes and much better too. I got tunneled visioned and didn't take a step back to
> look at the big picture. Thanks for the suggestion :-)
>
> I think we can make it more efficient by checking if
> sgs->group_misfit_task_load is set
>
>                 /* Check if task fits in the CPU */
>                 if (sd->flags & SD_ASYM_CPUCAPACITY &&
>                     sgs->group_misfit_task_load &&
>                     task_fits_cpu(p, i))
>                         sgs->group_misfit_task_load = 0;
>
> which will avoid calling task_fits_cpu() repeatedly if we got a hit already.

yes, looks better

>
>
> Thanks!
>
> --
> Qais Yousef
>
> >
> > -     /* Check if task fits in the group */
> > -     if (sd->flags & SD_ASYM_CPUCAPACITY &&
> > -         !task_fits_capacity(p, group->sgc->max_capacity)) {
> > -             sgs->group_misfit_task_load = 1;
> >       }
> >
> >       sgs->group_capacity = group->sgc->capacity;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 02c970501295..3292ad2db4ac 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -2988,6 +2988,15 @@ static inline bool uclamp_is_used(void)
> >       return static_branch_likely(&sched_uclamp_used);
> >  }
> >  #else /* CONFIG_UCLAMP_TASK */
> > +static inline unsigned long uclamp_eff_value(struct task_struct *p,
> > +                                          enum uclamp_id clamp_id)
> > +{
> > +     if (clamp_id == UCLAMP_MIN)
> > +             return 0;
> > +
> > +     return SCHED_CAPACITY_SCALE;
> > +}
> > +
> >  static inline
> >  unsigned long uclamp_rq_util_with(struct rq *rq, unsigned long util,
> >                                 struct task_struct *p)
> > --
> > 2.17.1
> >
> > >
> > > Thanks!
> > >
> > > --
> > > Qais Yousef