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SubjectRe: [PATCH 2/7] sched/uclamp: Make task_fits_capacity() use util_fits_cpu()
On 07/11/22 15:09, Vincent Guittot wrote:
> On Wed, 29 Jun 2022 at 21:48, Qais Yousef <qais.yousef@arm.com> wrote:

[...]

> > @@ -8502,15 +8504,16 @@ static void update_cpu_capacity(struct sched_domain *sd, int cpu)
> > trace_sched_cpu_capacity_tp(cpu_rq(cpu));
> >
> > sdg->sgc->capacity = capacity;
> > - sdg->sgc->min_capacity = capacity;
> > - sdg->sgc->max_capacity = capacity;
> > + sdg->sgc->min_capacity_cpu = cpu;
> > + sdg->sgc->max_capacity_cpu = cpu;
>
> you make these fields useless. There is only one cpu per sched_group
> at this level so you don't need to save the twice cpu number of the
> nly cpu of this group

Ah, so we can use group->asym_prefer_cpu then?

I think I got confused and thought we could cover multiple capacity levels
there.

> > }
> >
> > void update_group_capacity(struct sched_domain *sd, int cpu)
> > {
> > - struct sched_domain *child = sd->child;
> > struct sched_group *group, *sdg = sd->groups;
> > - unsigned long capacity, min_capacity, max_capacity;
> > + struct sched_domain *child = sd->child;
> > + int min_capacity_cpu, max_capacity_cpu;
> > + unsigned long capacity;
> > unsigned long interval;
> >
> > interval = msecs_to_jiffies(sd->balance_interval);
> > @@ -8523,8 +8526,7 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
> > }
> >
> > capacity = 0;
> > - min_capacity = ULONG_MAX;
> > - max_capacity = 0;
> > + min_capacity_cpu = max_capacity_cpu = cpu;
> >
> > if (child->flags & SD_OVERLAP) {
> > /*
> > @@ -8536,29 +8538,44 @@ void update_group_capacity(struct sched_domain *sd, int cpu)
> > unsigned long cpu_cap = capacity_of(cpu);
> >
> > capacity += cpu_cap;
> > - min_capacity = min(cpu_cap, min_capacity);
> > - max_capacity = max(cpu_cap, max_capacity);
> > + if (cpu_cap < capacity_of(min_capacity_cpu))
> > + min_capacity_cpu = cpu;
> > +
> > + if (cpu_cap > capacity_of(max_capacity_cpu))
> > + max_capacity_cpu = cpu;
> > }
> > } else {
> > /*
> > * !SD_OVERLAP domains can assume that child groups
> > * span the current group.
> > */
> > + unsigned long min_capacity = ULONG_MAX;
> > + unsigned long max_capacity = 0;
> >
> > group = child->groups;
> > do {
> > struct sched_group_capacity *sgc = group->sgc;
> > + unsigned long cpu_cap_min = capacity_of(sgc->min_capacity_cpu);
> > + unsigned long cpu_cap_max = capacity_of(sgc->max_capacity_cpu);
>
> By replacing sgc->min_capacity with sgc->min_capacity_cpu, the
> min_capacity is no more stable and can become > max_capacity

Right.

>
> >
> > capacity += sgc->capacity;
> > - min_capacity = min(sgc->min_capacity, min_capacity);
> > - max_capacity = max(sgc->max_capacity, max_capacity);
> > + if (cpu_cap_min < min_capacity) {
> > + min_capacity = cpu_cap_min;
> > + min_capacity_cpu = sgc->min_capacity_cpu;
> > + }
> > +
> > + if (cpu_cap_max > max_capacity) {
> > + max_capacity = cpu_cap_max;
> > + max_capacity_cpu = sgc->max_capacity_cpu;
> > + }
> > +
> > group = group->next;
> > } while (group != child->groups);
> > }
> >
> > sdg->sgc->capacity = capacity;
> > - sdg->sgc->min_capacity = min_capacity;
> > - sdg->sgc->max_capacity = max_capacity;
> > + sdg->sgc->min_capacity_cpu = min_capacity_cpu;
> > + sdg->sgc->max_capacity_cpu = max_capacity_cpu;
> > }
> >
> > /*
> > @@ -8902,7 +8919,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> > * internally or be covered by avg_load imbalance (eventually).
> > */
> > if (sgs->group_type == group_misfit_task &&
> > - (!capacity_greater(capacity_of(env->dst_cpu), sg->sgc->max_capacity) ||
> > + (!capacity_greater(env->dst_cpu, sg->sgc->max_capacity_cpu) ||
> > sds->local_stat.group_type != group_has_spare))
> > return false;
> >
> > @@ -8986,7 +9003,7 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> > */
> > if ((env->sd->flags & SD_ASYM_CPUCAPACITY) &&
> > (sgs->group_type <= group_fully_busy) &&
> > - (capacity_greater(sg->sgc->min_capacity, capacity_of(env->dst_cpu))))
> > + (capacity_greater(sg->sgc->min_capacity_cpu, env->dst_cpu)))
> > return false;
> >
> > return true;
> > @@ -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.


Thanks!

--
Qais Yousef

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