linux-kernel - [PATCH v3 3/5] sched/fair: Fix find_idlest

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Date:   Thu, 31 Aug 2017 12:58:00 +0100
From:   Brendan Jackman <brendan.jackman@....com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Josef Bacik <josef@...icpanda.com>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: [PATCH v3 3/5] 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@....com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Josef Bacik <josef@...icpanda.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Morten Rasmussen <morten.rasmussen@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.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 4ccecbf..0ce75bb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5387,8 +5387,9 @@ 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;
-- 
2.7.4