Commit 15d78f22 authored Mar 30, 2016 by Morten Rasmussen Committed by Chris Redpath Dec 19, 2017

ANDROID: 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.

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Change-Id: I89c0043fcc414f5e57eb6264b76b6137cc43c886
Signed-off-by: Chris Redpath <chris.redpath@arm.com>

parent a35c8cc0

kernel/sched/fair.c

+13 −1

Original line number	Diff line number	Diff line
		@@ -5594,6 +5594,7 @@ 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,
		@@ -5626,7 +5627,18 @@ 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;
		}

		/*