linux-kernel - [PATCH 5/8] sched/fair: Make check_misfit_status() only compare dynamic capacities

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Message-Id: <20210128183141.28097-6-valentin.schneider@arm.com>
Date:   Thu, 28 Jan 2021 18:31:38 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Qais Yousef <qais.yousef@....com>,
        Quentin Perret <qperret@...gle.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Rik van Riel <riel@...riel.com>
Subject: [PATCH 5/8] sched/fair: Make check_misfit_status() only compare dynamic capacities

check_misfit_status() checks for both capacity pressure & available CPUs
with higher capacity. Now that we have a sane(ish) capacity comparison
margin which is used throughout load-balance, this can be condensed into a
single check:

  capacity_greater(<root_domain max capacity>, <misfit task CPU's capacity>);

This has the added benefit of returning false if the misfit task CPU's is
heavily pressured, but there are no better candidates for migration.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/sched/fair.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0959a770ecc0..ef44474b8fbf 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8254,14 +8254,12 @@ check_cpu_capacity(struct rq *rq, struct sched_domain *sd)
 
 /*
  * Check whether a rq has a misfit task and if it looks like we can actually
- * help that task: we can migrate the task to a CPU of higher capacity, or
- * the task's current CPU is heavily pressured.
+ * help that task: we can migrate the task to a CPU of higher capacity.
  */
-static inline int check_misfit_status(struct rq *rq, struct sched_domain *sd)
+static inline int check_misfit_status(struct rq *rq)
 {
 	return rq->misfit_task_load &&
-		(capacity_greater(rq->rd->max_cpu_capacity, rq->cpu_capacity_orig) ||
-		 check_cpu_capacity(rq, sd));
+		capacity_greater(rq->rd->max_cpu_capacity, rq->cpu_capacity);
 }
 
 /*
@@ -10238,7 +10236,7 @@ static void nohz_balancer_kick(struct rq *rq)
 		 * When ASYM_CPUCAPACITY; see if there's a higher capacity CPU
 		 * to run the misfit task on.
 		 */
-		if (check_misfit_status(rq, sd)) {
+		if (check_misfit_status(rq)) {
 			flags = NOHZ_KICK_MASK;
 			goto unlock;
 		}
-- 
2.27.0