Re: [PATCH 2/2 v5] sched/fair: Remove capacity inversion detection

[Vincent Guittot]

On Sat, 4 Feb 2023 at 19:42, Qais Yousef <qyousef@xxxxxxxxxxx> wrote:
>
> On 02/01/23 15:36, Vincent Guittot wrote:
> > Remove the capacity inversion detection which is now handled by
> > util_fits_cpu() returning -1 when we need to continue to look for a
> > potential CPU with better performance.
> >
> > This ends up almost reverting patches below except for some comments:
>
> nit: I think this comment must be removed/reworeded though

This comment has already been removed. That's why I said almost revert
except for some comments in the commit message

>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 691a2f9c4efa..c6c8e7f52935 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4476,10 +4476,6 @@ static inline int util_fits_cpu(unsigned long util,
>          *
>          * For uclamp_max, we can tolerate a drop in performance level as the
>          * goal is to cap the task. So it's okay if it's getting less.
> -        *
> -        * In case of capacity inversion, which is not handled yet, we should
> -        * honour the inverted capacity for both uclamp_min and uclamp_max all
> -        * the time.
>          */
>         capacity_orig = capacity_orig_of(cpu);
>         capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
>
> > commit da07d2f9c153 ("sched/fair: Fixes for capacity inversion detection")
> > commit aa69c36f31aa ("sched/fair: Consider capacity inversion in util_fits_cpu()")
> > commit 44c7b80bffc3 ("sched/fair: Detect capacity inversion")
> >
> > Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>
> Apart from that, LGTM.
>
> Reviewed-by: Qais Yousef <qyousef@xxxxxxxxxxx>

Thanks

>
>
> Thanks!
>
> --
> Qais Yousef
>
> > ---
> >  kernel/sched/fair.c  | 84 +++-----------------------------------------
> >  kernel/sched/sched.h | 19 ----------
> >  2 files changed, 5 insertions(+), 98 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 074742f107c0..c6c8e7f52935 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -4476,17 +4476,9 @@ static inline int util_fits_cpu(unsigned long util,
> >        *
> >        * For uclamp_max, we can tolerate a drop in performance level as the
> >        * goal is to cap the task. So it's okay if it's getting less.
> > -      *
> > -      * In case of capacity inversion we should honour the inverted capacity
> > -      * for both uclamp_min and uclamp_max all the time.
> >        */
> > -     capacity_orig = cpu_in_capacity_inversion(cpu);
> > -     if (capacity_orig) {
> > -             capacity_orig_thermal = capacity_orig;
> > -     } else {
> > -             capacity_orig = capacity_orig_of(cpu);
> > -             capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
> > -     }
> > +     capacity_orig = capacity_orig_of(cpu);
> > +     capacity_orig_thermal = capacity_orig - arch_scale_thermal_pressure(cpu);
> >
> >       /*
> >        * We want to force a task to fit a cpu as implied by uclamp_max.
> > @@ -9027,82 +9019,16 @@ static unsigned long scale_rt_capacity(int cpu)
> >
> >  static void update_cpu_capacity(struct sched_domain *sd, int cpu)
> >  {
> > -     unsigned long capacity_orig = arch_scale_cpu_capacity(cpu);
> >       unsigned long capacity = scale_rt_capacity(cpu);
> >       struct sched_group *sdg = sd->groups;
> > -     struct rq *rq = cpu_rq(cpu);
> >
> > -     rq->cpu_capacity_orig = capacity_orig;
> > +     cpu_rq(cpu)->cpu_capacity_orig = arch_scale_cpu_capacity(cpu);
> >
> >       if (!capacity)
> >               capacity = 1;
> >
> > -     rq->cpu_capacity = capacity;
> > -
> > -     /*
> > -      * Detect if the performance domain is in capacity inversion state.
> > -      *
> > -      * Capacity inversion happens when another perf domain with equal or
> > -      * lower capacity_orig_of() ends up having higher capacity than this
> > -      * domain after subtracting thermal pressure.
> > -      *
> > -      * We only take into account thermal pressure in this detection as it's
> > -      * the only metric that actually results in *real* reduction of
> > -      * capacity due to performance points (OPPs) being dropped/become
> > -      * unreachable due to thermal throttling.
> > -      *
> > -      * We assume:
> > -      *   * That all cpus in a perf domain have the same capacity_orig
> > -      *     (same uArch).
> > -      *   * Thermal pressure will impact all cpus in this perf domain
> > -      *     equally.
> > -      */
> > -     if (sched_energy_enabled()) {
> > -             unsigned long inv_cap = capacity_orig - thermal_load_avg(rq);
> > -             struct perf_domain *pd;
> > -
> > -             rcu_read_lock();
> > -
> > -             pd = rcu_dereference(rq->rd->pd);
> > -             rq->cpu_capacity_inverted = 0;
> > -
> > -             for (; pd; pd = pd->next) {
> > -                     struct cpumask *pd_span = perf_domain_span(pd);
> > -                     unsigned long pd_cap_orig, pd_cap;
> > -
> > -                     /* We can't be inverted against our own pd */
> > -                     if (cpumask_test_cpu(cpu_of(rq), pd_span))
> > -                             continue;
> > -
> > -                     cpu = cpumask_any(pd_span);
> > -                     pd_cap_orig = arch_scale_cpu_capacity(cpu);
> > -
> > -                     if (capacity_orig < pd_cap_orig)
> > -                             continue;
> > -
> > -                     /*
> > -                      * handle the case of multiple perf domains have the
> > -                      * same capacity_orig but one of them is under higher
> > -                      * thermal pressure. We record it as capacity
> > -                      * inversion.
> > -                      */
> > -                     if (capacity_orig == pd_cap_orig) {
> > -                             pd_cap = pd_cap_orig - thermal_load_avg(cpu_rq(cpu));
> > -
> > -                             if (pd_cap > inv_cap) {
> > -                                     rq->cpu_capacity_inverted = inv_cap;
> > -                                     break;
> > -                             }
> > -                     } else if (pd_cap_orig > inv_cap) {
> > -                             rq->cpu_capacity_inverted = inv_cap;
> > -                             break;
> > -                     }
> > -             }
> > -
> > -             rcu_read_unlock();
> > -     }
> > -
> > -     trace_sched_cpu_capacity_tp(rq);
> > +     cpu_rq(cpu)->cpu_capacity = capacity;
> > +     trace_sched_cpu_capacity_tp(cpu_rq(cpu));
> >
> >       sdg->sgc->capacity = capacity;
> >       sdg->sgc->min_capacity = capacity;
> > diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> > index 1072502976df..3e8df6d31c1e 100644
> > --- a/kernel/sched/sched.h
> > +++ b/kernel/sched/sched.h
> > @@ -1044,7 +1044,6 @@ struct rq {
> >
> >       unsigned long           cpu_capacity;
> >       unsigned long           cpu_capacity_orig;
> > -     unsigned long           cpu_capacity_inverted;
> >
> >       struct balance_callback *balance_callback;
> >
> > @@ -2899,24 +2898,6 @@ static inline unsigned long capacity_orig_of(int cpu)
> >       return cpu_rq(cpu)->cpu_capacity_orig;
> >  }
> >
> > -/*
> > - * Returns inverted capacity if the CPU is in capacity inversion state.
> > - * 0 otherwise.
> > - *
> > - * Capacity inversion detection only considers thermal impact where actual
> > - * performance points (OPPs) gets dropped.
> > - *
> > - * Capacity inversion state happens when another performance domain that has
> > - * equal or lower capacity_orig_of() becomes effectively larger than the perf
> > - * domain this CPU belongs to due to thermal pressure throttling it hard.
> > - *
> > - * See comment in update_cpu_capacity().
> > - */
> > -static inline unsigned long cpu_in_capacity_inversion(int cpu)
> > -{
> > -     return cpu_rq(cpu)->cpu_capacity_inverted;
> > -}
> > -
> >  /**
> >   * enum cpu_util_type - CPU utilization type
> >   * @FREQUENCY_UTIL:  Utilization used to select frequency
> > --
> > 2.34.1
> >