linux-kernel - [PATCH 3/3] sched/fair: Kill wake

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Date:   Fri, 24 Jan 2020 12:42:55 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, morten.rasmussen@....com,
        qperret@...gle.com, adharmap@...eaurora.org
Subject: [PATCH 3/3] sched/fair: Kill wake_cap()

From: Morten Rasmussen <morten.rasmussen@....com>

Capacity-awareness in the wake-up path previously involved disabling
wake_affine in certain scenarios. We have just made select_idle_sibling()
capacity-aware, so this isn't needed anymore.

Remove wake_cap() entirely.

Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
[Changelog tweaks]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/fair.c | 30 +-----------------------------
 1 file changed, 1 insertion(+), 29 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 47a4f52d89b44..e21ce8f2186a4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6124,33 +6124,6 @@ static unsigned long cpu_util_without(int cpu, struct task_struct *p)
 	return min_t(unsigned long, util, capacity_orig_of(cpu));
 }
 
-/*
- * Disable WAKE_AFFINE in the case where task @p doesn't fit in the
- * capacity of either the waking CPU @cpu or the previous CPU @prev_cpu.
- *
- * In that case WAKE_AFFINE doesn't make sense and we'll let
- * BALANCE_WAKE sort things out.
- */
-static int wake_cap(struct task_struct *p, int cpu, int prev_cpu)
-{
-	long min_cap, max_cap;
-
-	if (!static_branch_unlikely(&sched_asym_cpucapacity))
-		return 0;
-
-	min_cap = min(capacity_orig_of(prev_cpu), capacity_orig_of(cpu));
-	max_cap = cpu_rq(cpu)->rd->max_cpu_capacity;
-
-	/* Minimum capacity is close to max, no need to abort wake_affine */
-	if (max_cap - min_cap < max_cap >> 3)
-		return 0;
-
-	/* Bring task utilization in sync with prev_cpu */
-	sync_entity_load_avg(&p->se);
-
-	return !task_fits_capacity(p, min_cap);
-}
-
 /*
  * Predicts what cpu_util(@cpu) would return if @p was migrated (and enqueued)
  * to @dst_cpu.
@@ -6415,8 +6388,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_f
 			new_cpu = prev_cpu;
 		}
 
-		want_affine = !wake_wide(p) && !wake_cap(p, cpu, prev_cpu) &&
-			      cpumask_test_cpu(cpu, p->cpus_ptr);
+		want_affine = !wake_wide(p) && cpumask_test_cpu(cpu, p->cpus_ptr);
 	}
 
 	rcu_read_lock();
-- 
2.24.0