Re: [PATCH 7/8] sched/eevdf: Compare min slice during wake_affine

[Kayra Cizmeci <kayracizmeci@gmail.com>]

Hi Vincent,

> Add a new level in wake affine where we check on which CPU the task
> would most probably run 1st between this and prev CPUs.

> @@ -8402,6 +8402,9 @@ static int wake_wide(struct task_struct *p)
>   * wake_affine_idle() - only considers 'now', it check if the waking CPU is
>   *			cache-affine and is (or	will be) idle.
>   *
> + * wake_affine_slice() - only considers 'now', it check if the waking CPU can
> + *			 be preempted because using longer slice.
> + *
>   * wake_affine_weight() - considers the weight to reflect the average
>   *			  scheduling latency of the CPUs. This seems to work
>   *			  for the overloaded case.
> @@ -8437,6 +8440,20 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
>  	return nr_cpumask_bits;
>  }

> +static int
> +wake_affine_slice(struct task_struct *p, int this_cpu, int prev_cpu)
> +{
> +	struct sched_entity *se = &p->se;
> +
> +	if (se->slice < get_rq_min_slice(cpu_rq(prev_cpu)))
> +		return prev_cpu;
> +
> +	if (se->slice < get_rq_min_slice(cpu_rq(this_cpu)))
> +		return this_cpu;
> +
> +	return nr_cpumask_bits;
> +}
> +
>  static int
>  wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
>  		   int this_cpu, int prev_cpu, int sync)
> @@ -8488,6 +8505,9 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p,
>  	if (sched_feat(WA_IDLE))
>  		target = wake_affine_idle(this_cpu, prev_cpu, sync);
>  
> +	if (sched_feat(PREEMPT_SHORT) && target == nr_cpumask_bits)
> +		target = wake_affine_slice(p, this_cpu, prev_cpu);
> +
>  	if (sched_feat(WA_WEIGHT) && target == nr_cpumask_bits)
>  		target = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);
>  
> -- 
> 2.53.0

this_cpu has min_slice of 7 while prev_cpu has min_slice of 5.
se->slice == 4, so on wake_affine_slice() prev_cpu is chosen.

Ain't getting onto a cpu with bigger min_slice is better for us?
If so, is this works for you?


diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 09f0667e97a2..e50c339e5c2d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8444,14 +8444,13 @@ static int
 wake_affine_slice(struct task_struct *p, int this_cpu, int prev_cpu)
 {
 	struct sched_entity *se = &p->se;
+	u64 min_prev = get_rq_min_slice(cpu_rq(prev_cpu));
+	u64 min_this = get_rq_min_slice(cpu_rq(this_cpu));
 
-	if (se->slice < get_rq_min_slice(cpu_rq(prev_cpu)))
-		return prev_cpu;
-
-	if (se->slice < get_rq_min_slice(cpu_rq(this_cpu)))
-		return this_cpu;
+	if (se->slice >= max(min_prev, min_this))
+		return nr_cpumask_bits;
 
-	return nr_cpumask_bits;
+	return min_prev >= min_this ? prev_cpu : this_cpu;
 }
 
 static int

Thanks, 
Kayra