linux-kernel - [PATCH 09/11] sched/fair: Split out helper to adjust imbalances between domains

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Date:   Wed, 12 Feb 2020 15:45:32 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Phil Auld <pauld@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 09/11] sched/fair: Split out helper to adjust imbalances
 between domains

The patch "sched/fair: Allow a small load imbalance between low utilisation
SD_NUMA domains" allows an imbalance when the busiest group has very
few tasks. Move the check to a helper function as it is needed by a later
patch.

No functional change.

Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
---
 kernel/sched/fair.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 24fc90b8036a..b2476ef0b056 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8758,6 +8758,21 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
 	}
 }
 
+static inline long adjust_numa_imbalance(int imbalance, int src_nr_running)
+{
+	unsigned int imbalance_min;
+
+	/*
+	 * Allow a small imbalance based on a simple pair of communicating
+	 * tasks that remain local when the source domain is almost idle.
+	 */
+	imbalance_min = 2;
+	if (src_nr_running <= imbalance_min)
+		return 0;
+
+	return imbalance;
+}
+
 /**
  * calculate_imbalance - Calculate the amount of imbalance present within the
  *			 groups of a given sched_domain during load balance.
@@ -8854,18 +8869,9 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		}
 
 		/* Consider allowing a small imbalance between NUMA groups */
-		if (env->sd->flags & SD_NUMA) {
-			unsigned int imbalance_min;
-
-			/*
-			 * Allow a small imbalance based on a simple pair of
-			 * communicating tasks that remain local when the
-			 * source domain is almost idle.
-			 */
-			imbalance_min = 2;
-			if (busiest->sum_nr_running <= imbalance_min)
-				env->imbalance = 0;
-		}
+		if (env->sd->flags & SD_NUMA)
+			env->imbalance = adjust_numa_imbalance(env->imbalance,
+						busiest->sum_nr_running);
 
 		return;
 	}
-- 
2.16.4