Re: [PATCH] sched/fair: Remove SIS_PROP

[Yicong Yang]

On 2023/10/20 21:43, Peter Zijlstra 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>

SIS_UTIL works fine on my machine, so

Reviewed-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>

> ---
>  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;
>  
>