linux-kernel - Re: [PATCH v3 04/10] sched/fair: rework load

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Date:   Tue, 1 Oct 2019 10:15:25 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org
Cc:     pauld@...hat.com, valentin.schneider@....com,
        srikar@...ux.vnet.ibm.com, quentin.perret@....com,
        Morten.Rasmussen@....com, hdanton@...a.com
Subject: Re: [PATCH v3 04/10] sched/fair: rework load_balance

On 19/09/2019 09:33, Vincent Guittot wrote:


[...]

> @@ -8042,14 +8104,24 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>  		}
>  	}
>  
> -	/* Adjust by relative CPU capacity of the group */
> +	/* Check if dst cpu is idle and preferred to this group */
> +	if (env->sd->flags & SD_ASYM_PACKING &&
> +	    env->idle != CPU_NOT_IDLE &&
> +	    sgs->sum_h_nr_running &&
> +	    sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) {
> +		sgs->group_asym_packing = 1;
> +	}
> +

Since asym_packing check is done per-sg rather per-CPU (like misfit_task), can you
not check for asym_packing in group_classify() directly (like for overloaded) and
so get rid of struct sg_lb_stats::group_asym_packing?

Something like (only compile tested).

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d0c3aa1dc290..b2848d6f8a2a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7692,7 +7692,6 @@ struct sg_lb_stats {
        unsigned int idle_cpus;
        unsigned int group_weight;
        enum group_type group_type;
-       unsigned int group_asym_packing; /* Tasks should be moved to preferred CPU */
        unsigned long group_misfit_task_load; /* A CPU has a task too big for its capacity */
 #ifdef CONFIG_NUMA_BALANCING
        unsigned int nr_numa_running;
@@ -7952,6 +7951,20 @@ group_is_overloaded(struct lb_env *env, struct sg_lb_stats *sgs)
        return false;
 }
 
+static inline bool
+group_has_asym_packing(struct lb_env *env, struct sched_group *sg,
+                      struct sg_lb_stats *sgs)
+{
+       if (env->sd->flags & SD_ASYM_PACKING &&
+           env->idle != CPU_NOT_IDLE &&
+           sgs->sum_h_nr_running &&
+           sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
+               return true;
+       }
+
+       return false;
+}
+
 /*
  * group_smaller_min_cpu_capacity: Returns true if sched_group sg has smaller
  * per-CPU capacity than sched_group ref.
@@ -7983,7 +7996,7 @@ group_type group_classify(struct lb_env *env,
        if (sg_imbalanced(group))
                return group_imbalanced;
 
-       if (sgs->group_asym_packing)
+       if (group_has_asym_packing(env, group, sgs))
                return group_asym_packing;
 
        if (sgs->group_misfit_task_load)
@@ -8076,14 +8089,6 @@ static inline void update_sg_lb_stats(struct lb_env *env,
                }
        }
 
-       /* Check if dst cpu is idle and preferred to this group */
-       if (env->sd->flags & SD_ASYM_PACKING &&
-           env->idle != CPU_NOT_IDLE &&
-           sgs->sum_h_nr_running &&
-           sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) {
-               sgs->group_asym_packing = 1;
-       }
-
        sgs->group_capacity = group->sgc->capacity;

[...]