Re: [PATCH] sched/fair: Remove SIS_PROP

[Vincent Guittot]

On Fri, 20 Oct 2023 at 15:44, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
>
>
> Since this had me looking at all that code, I did the below.
>
> Holler if there's objections etc..
>
> ---
> Subject: sched/fair: Remove SIS_PROP
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Fri Oct 20 12:35:33 CEST 2023
>
> SIS_UTIL seems to work well, lets remove the old thing.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Acked-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

> ---
>  include/linux/sched/topology.h |    2 -
>  kernel/sched/core.c            |    5 ----
>  kernel/sched/fair.c            |   48 -----------------------------------------
>  kernel/sched/features.h        |    1
>  kernel/sched/sched.h           |    3 --
>  5 files changed, 59 deletions(-)
>
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -109,8 +109,6 @@ struct sched_domain {
>         u64 max_newidle_lb_cost;
>         unsigned long last_decay_max_lb_cost;
>
> -       u64 avg_scan_cost;              /* select_idle_sibling */
> -
>  #ifdef CONFIG_SCHEDSTATS
>         /* load_balance() stats */
>         unsigned int lb_count[CPU_MAX_IDLE_TYPES];
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3792,9 +3792,6 @@ ttwu_do_activate(struct rq *rq, struct t
>                 if (rq->avg_idle > max)
>                         rq->avg_idle = max;
>
> -               rq->wake_stamp = jiffies;
> -               rq->wake_avg_idle = rq->avg_idle / 2;
> -
>                 rq->idle_stamp = 0;
>         }
>  #endif
> @@ -9991,8 +9988,6 @@ void __init sched_init(void)
>                 rq->online = 0;
>                 rq->idle_stamp = 0;
>                 rq->avg_idle = 2*sysctl_sched_migration_cost;
> -               rq->wake_stamp = jiffies;
> -               rq->wake_avg_idle = rq->avg_idle;
>                 rq->max_idle_balance_cost = sysctl_sched_migration_cost;
>
>                 INIT_LIST_HEAD(&rq->cfs_tasks);
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7209,45 +7209,9 @@ static int select_idle_cpu(struct task_s
>         struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_rq_mask);
>         int i, cpu, idle_cpu = -1, nr = INT_MAX;
>         struct sched_domain_shared *sd_share;
> -       struct rq *this_rq = this_rq();
> -       int this = smp_processor_id();
> -       struct sched_domain *this_sd = NULL;
> -       u64 time = 0;
>
>         cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>
> -       if (sched_feat(SIS_PROP) && !has_idle_core) {
> -               u64 avg_cost, avg_idle, span_avg;
> -               unsigned long now = jiffies;
> -
> -               this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
> -               if (!this_sd)
> -                       return -1;
> -
> -               /*
> -                * If we're busy, the assumption that the last idle period
> -                * predicts the future is flawed; age away the remaining
> -                * predicted idle time.
> -                */
> -               if (unlikely(this_rq->wake_stamp < now)) {
> -                       while (this_rq->wake_stamp < now && this_rq->wake_avg_idle) {
> -                               this_rq->wake_stamp++;
> -                               this_rq->wake_avg_idle >>= 1;
> -                       }
> -               }
> -
> -               avg_idle = this_rq->wake_avg_idle;
> -               avg_cost = this_sd->avg_scan_cost + 1;
> -
> -               span_avg = sd->span_weight * avg_idle;
> -               if (span_avg > 4*avg_cost)
> -                       nr = div_u64(span_avg, avg_cost);
> -               else
> -                       nr = 4;
> -
> -               time = cpu_clock(this);
> -       }
> -
>         if (sched_feat(SIS_UTIL)) {
>                 sd_share = rcu_dereference(per_cpu(sd_llc_shared, target));
>                 if (sd_share) {
> @@ -7301,18 +7265,6 @@ static int select_idle_cpu(struct task_s
>         if (has_idle_core)
>                 set_idle_cores(target, false);
>
> -       if (sched_feat(SIS_PROP) && this_sd && !has_idle_core) {
> -               time = cpu_clock(this) - time;
> -
> -               /*
> -                * Account for the scan cost of wakeups against the average
> -                * idle time.
> -                */
> -               this_rq->wake_avg_idle -= min(this_rq->wake_avg_idle, time);
> -
> -               update_avg(&this_sd->avg_scan_cost, time);
> -       }
> -
>         return idle_cpu;
>  }
>
> --- a/kernel/sched/features.h
> +++ b/kernel/sched/features.h
> @@ -49,7 +49,6 @@ SCHED_FEAT(TTWU_QUEUE, true)
>  /*
>   * When doing wakeups, attempt to limit superfluous scans of the LLC domain.
>   */
> -SCHED_FEAT(SIS_PROP, false)
>  SCHED_FEAT(SIS_UTIL, true)
>
>  /*
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1059,9 +1059,6 @@ struct rq {
>         u64                     idle_stamp;
>         u64                     avg_idle;
>
> -       unsigned long           wake_stamp;
> -       u64                     wake_avg_idle;
> -
>         /* This is used to determine avg_idle's max value */
>         u64                     max_idle_balance_cost;
>
>
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