linux-kernel - Re: [PATCH 3/5] sched/fair: rework load

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Date:   Fri, 19 Jul 2019 14:54:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        quentin.perret@....com, dietmar.eggemann@....com,
        Morten.Rasmussen@....com, pauld@...hat.com
Subject: Re: [PATCH 3/5] sched/fair: rework load_balance

On Fri, Jul 19, 2019 at 09:58:23AM +0200, Vincent Guittot wrote:

> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 67f0acd..472959df 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5376,18 +5376,6 @@ static unsigned long capacity_of(int cpu)
>  	return cpu_rq(cpu)->cpu_capacity;
>  }
>  
> -static unsigned long cpu_avg_load_per_task(int cpu)
> -{
> -	struct rq *rq = cpu_rq(cpu);
> -	unsigned long nr_running = READ_ONCE(rq->cfs.h_nr_running);
> -	unsigned long load_avg = cpu_runnable_load(rq);
> -
> -	if (nr_running)
> -		return load_avg / nr_running;
> -
> -	return 0;
> -}
> -
>  static void record_wakee(struct task_struct *p)
>  {
>  	/*

> @@ -7646,7 +7669,6 @@ static unsigned long task_h_load(struct task_struct *p)
>  struct sg_lb_stats {
>  	unsigned long avg_load; /*Avg load across the CPUs of the group */
>  	unsigned long group_load; /* Total load over the CPUs of the group */
> -	unsigned long load_per_task;
>  	unsigned long group_capacity;
>  	unsigned long group_util; /* Total utilization of the group */
>  	unsigned int sum_nr_running; /* Nr tasks running in the group */


> @@ -8266,76 +8293,6 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
>  }
>  
>  /**
> - * fix_small_imbalance - Calculate the minor imbalance that exists
> - *			amongst the groups of a sched_domain, during
> - *			load balancing.
> - * @env: The load balancing environment.
> - * @sds: Statistics of the sched_domain whose imbalance is to be calculated.
> - */
> -static inline
> -void fix_small_imbalance(struct lb_env *env, struct sd_lb_stats *sds)
> -{
> -	unsigned long tmp, capa_now = 0, capa_move = 0;
> -	unsigned int imbn = 2;
> -	unsigned long scaled_busy_load_per_task;
> -	struct sg_lb_stats *local, *busiest;
> -
> -	local = &sds->local_stat;
> -	busiest = &sds->busiest_stat;
> -
> -	if (!local->sum_h_nr_running)
> -		local->load_per_task = cpu_avg_load_per_task(env->dst_cpu);
> -	else if (busiest->load_per_task > local->load_per_task)
> -		imbn = 1;
> -
> -	scaled_busy_load_per_task =
> -		(busiest->load_per_task * SCHED_CAPACITY_SCALE) /
> -		busiest->group_capacity;
> -
> -	if (busiest->avg_load + scaled_busy_load_per_task >=
> -	    local->avg_load + (scaled_busy_load_per_task * imbn)) {
> -		env->imbalance = busiest->load_per_task;
> -		return;
> -	}
> -
> -	/*
> -	 * OK, we don't have enough imbalance to justify moving tasks,
> -	 * however we may be able to increase total CPU capacity used by
> -	 * moving them.
> -	 */
> -
> -	capa_now += busiest->group_capacity *
> -			min(busiest->load_per_task, busiest->avg_load);
> -	capa_now += local->group_capacity *
> -			min(local->load_per_task, local->avg_load);
> -	capa_now /= SCHED_CAPACITY_SCALE;
> -
> -	/* Amount of load we'd subtract */
> -	if (busiest->avg_load > scaled_busy_load_per_task) {
> -		capa_move += busiest->group_capacity *
> -			    min(busiest->load_per_task,
> -				busiest->avg_load - scaled_busy_load_per_task);
> -	}
> -
> -	/* Amount of load we'd add */
> -	if (busiest->avg_load * busiest->group_capacity <
> -	    busiest->load_per_task * SCHED_CAPACITY_SCALE) {
> -		tmp = (busiest->avg_load * busiest->group_capacity) /
> -		      local->group_capacity;
> -	} else {
> -		tmp = (busiest->load_per_task * SCHED_CAPACITY_SCALE) /
> -		      local->group_capacity;
> -	}
> -	capa_move += local->group_capacity *
> -		    min(local->load_per_task, local->avg_load + tmp);
> -	capa_move /= SCHED_CAPACITY_SCALE;
> -
> -	/* Move if we gain throughput */
> -	if (capa_move > capa_now)
> -		env->imbalance = busiest->load_per_task;
> -}
> -
> -/**
>   * calculate_imbalance - Calculate the amount of imbalance present within the
>   *			 groups of a given sched_domain during load balance.
>   * @env: load balance environment

Maybe strip this out first, in a separate patch. It's all magic doo-doo.