[tip:sched/core] sched/fair: Fix find_idlest_group() when local group is not allowed

tip-bot for Brendan Jackman
2017-10-10T11:05:27Z

Commit-ID: 0d10ab952e99f3e9f374898e93f45452b81e5711
Gitweb: https://git.kernel.org/tip/0d10ab952e99f3e9f374898e93f45452b81e5711
Author: Brendan Jackman <brendan.jackman@arm.com>
AuthorDate: Thu, 5 Oct 2017 12:45:14 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 10 Oct 2017 11:45:34 +0200

sched/fair: Fix find_idlest_group() when local group is not allowed

When the local group is not allowed we do not modify this_*_load from
their initial value of 0. That means that the load checks at the end
of find_idlest_group cause us to incorrectly return NULL. Fixing the
initial values to ULONG_MAX means we will instead return the idlest
remote group in that case.

Signed-off-by: Brendan Jackman <brendan.jackman@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171005114516.18617-4-brendan.jackman@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bdd28fb..cca1835 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5737,8 +5737,9 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
{
struct sched_group *idlest = NULL, *group = sd->groups;
struct sched_group *most_spare_sg = NULL;
- unsigned long min_runnable_load = ULONG_MAX, this_runnable_load = 0;
- unsigned long min_avg_load = ULONG_MAX, this_avg_load = 0;
+ unsigned long min_runnable_load = ULONG_MAX;
+ unsigned long this_runnable_load = ULONG_MAX;
+ unsigned long min_avg_load = ULONG_MAX, this_avg_load = ULONG_MAX;
unsigned long most_spare = 0, this_spare = 0;
int load_idx = sd->forkexec_idx;
int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;