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From 91820aa3145f93421c29834315616f338b4fcca2 Mon Sep 17 00:00:00 2001
From: Morten Rasmussen <morten.rasmussen@arm.com>
Date: Wed, 30 Mar 2016 14:20:12 +0100
Subject: [PATCH 58/92] sched/fair: Add energy_diff dead-zone margin
It is not worth the overhead to migrate tasks for tiny insignificant
energy savings. To prevent this, an energy margin is introduced in
energy_diff() which effectively adds a dead-zone that rounds tiny energy
differences to zero. Since no scale is enforced for energy model data
the margin can't be absolute. Instead it is defined as +/-1.56% energy
saving compared to the current total estimated energy consumption.
(cherry picked from commit c36ecf27db72f60934ce2c9ca7e3d97a80926c1c)
Signed-off-by: Gaku Inami <gaku.inami.xw@bp.renesas.com>
---
kernel/sched/fair.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 799e2b5..5e13787 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5556,6 +5556,7 @@ static int energy_diff(struct energy_env *eenv)
struct sched_domain *sd;
struct sched_group *sg;
int sd_cpu = -1, energy_before = 0, energy_after = 0;
+ int diff, margin;
struct energy_env eenv_before = {
.util_delta = 0,
@@ -5588,7 +5589,18 @@ static int energy_diff(struct energy_env *eenv)
}
} while (sg = sg->next, sg != sd->groups);
- return energy_after-energy_before;
+ /*
+ * Dead-zone margin preventing too many migrations.
+ */
+
+ margin = energy_before >> 6; /* ~1.56% */
+
+ diff = energy_after-energy_before;
+
+ if (abs(diff) < margin)
+ return 0;
+
+ return diff;
}
/*
--
1.9.1
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