linux-kernel - Re: [PATCH 3/3] sched/fair: fix unnecessary increase of balance interval

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Date:   Thu, 13 Dec 2018 14:52:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        valentin.schneider@....com, Morten.Rasmussen@....com
Subject: Re: [PATCH 3/3] sched/fair: fix unnecessary increase of balance
 interval

On Tue, Aug 07, 2018 at 05:56:27PM +0200, Vincent Guittot wrote:
> +static inline bool
> +asym_active_balance(enum cpu_idle_type idle, unsigned int flags, int dst, int src)
>  {
> +	if (idle != CPU_NOT_IDLE) {
>  
>  		/*
>  		 * ASYM_PACKING needs to force migrate tasks from busy but
>  		 * lower priority CPUs in order to pack all tasks in the
>  		 * highest priority CPUs.
>  		 */
> +		if ((flags & SD_ASYM_PACKING) &&
> +		    sched_asym_prefer(dst, src))
> +			return true;
>  	}
>  
> +	return false;
> +}
> +
> +static int need_active_balance(struct lb_env *env)
> +{
> +	struct sched_domain *sd = env->sd;
> +
> +
> +	if (asym_active_balance(env->idle, sd->flags, env->dst_cpu, env->src_cpu))
> +		return 1;
> +
>  	/*
>  	 * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
>  	 * It's worth migrating the task if the src_cpu's capacity is reduced
> @@ -8650,7 +8660,8 @@ static int load_balance(int this_cpu, struct rq *this_rq,
>  	} else
>  		sd->nr_balance_failed = 0;
>  
> +	if (likely(!active_balance) ||
> +	    asym_active_balance(env.idle, sd->flags, env.dst_cpu, env.src_cpu)) {

Perhaps like the below?

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8857,21 +8857,24 @@ static struct rq *find_busiest_queue(str
  */
 #define MAX_PINNED_INTERVAL	512
 
+static inline bool
+asym_active_balance(struct lb_env *env)
+{
+	/*
+	 * ASYM_PACKING needs to force migrate tasks from busy but
+	 * lower priority CPUs in order to pack all tasks in the
+	 * highest priority CPUs.
+	 */
+	return env->idle != CPU_NOT_IDLE && (env->sd->flags & SD_ASYM_PACKING) &&
+		sched_asym_prefer(env->dst_cpu, env->src_cpu);
+}
+
 static int need_active_balance(struct lb_env *env)
 {
 	struct sched_domain *sd = env->sd;
 
-	if (env->idle != CPU_NOT_IDLE) {
-
-		/*
-		 * ASYM_PACKING needs to force migrate tasks from busy but
-		 * lower priority CPUs in order to pack all tasks in the
-		 * highest priority CPUs.
-		 */
-		if ((sd->flags & SD_ASYM_PACKING) &&
-		    sched_asym_prefer(env->dst_cpu, env->src_cpu))
-			return 1;
-	}
+	if (asym_active_balance(env))
+		return 1;
 
 	/*
 	 * The dst_cpu is idle and the src_cpu CPU has only 1 CFS task.
@@ -9150,7 +9153,7 @@ static int load_balance(int this_cpu, st
 	} else
 		sd->nr_balance_failed = 0;
 
-	if (likely(!active_balance)) {
+	if (likely(!active_balance) || asym_active_balance(&env)) {
 		/* We were unbalanced, so reset the balancing interval */
 		sd->balance_interval = sd->min_interval;
 	} else {