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sched/fair: Add energy_diff dead-zone margin

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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.

Change-Id: I6be069c752c701fb825430896b3b768a7ab2fee4
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
[rebase: on top of msm-google/android-msm-marlin-3.18,
         massage original patch which changes code in energy_diff()
	 into __energy_diff() introduced by SchedTune]
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
(cherry picked from commit 780cb5a5fa47adf13d4fc2b77e8e94448cd56098)
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
This commit is contained in:
Morten Rasmussen 2016-03-30 14:20:12 +01:00 • committed by Andres Oportus
parent 3b6ba235bc
commit 02cbde61f4
1 changed files with 11 additions and 0 deletions
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11
kernel/sched/fair.c
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@ -5149,6 +5149,7 @@ static inline 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,
@ -5198,6 +5199,16 @@ static inline int __energy_diff(struct energy_env *eenv)
eenv->cap.before, eenv->cap.after, eenv->cap.delta,
eenv->nrg.delta, eenv->payoff);
/*
* Dead-zone margin preventing too many migrations.
*/
margin = eenv->nrg.before >> 6; /* ~1.56% */
diff = eenv->nrg.after - eenv->nrg.before;
eenv->nrg.diff = (abs(diff) < margin) ? 0 : eenv->nrg.diff;
return eenv->nrg.diff;
}