Commit 6fee85cc authored Oct 05, 2017 by Brendan Jackman Committed by Ingo Molnar Oct 10, 2017

sched/fair: Fix usage of find_idlest_group() when no groups are allowed



When 'p' is not allowed on any of the CPUs in the sched_domain, we
currently return NULL from find_idlest_group(), and pointlessly
continue the search on lower sched_domain levels (where 'p' is also not
allowed) before returning prev_cpu regardless (as we have not updated
new_cpu).

Add an explicit check for this case, and add a comment to
find_idlest_group(). Now when find_idlest_group() returns NULL, it always
means that the local group is allowed and idlest.

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/20171005114516.18617-5-brendan.jackman@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 0d10ab95

kernel/sched/fair.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -5730,6 +5730,8 @@ static unsigned long capacity_spare_wake(int cpu, struct task_struct *p)
		/*
		* find_idlest_group finds and returns the least busy CPU group within the
		* domain.
		*
		* Assumes p is allowed on at least one CPU in sd.
		*/
		static struct sched_group *
		find_idlest_group(struct sched_domain sd, struct task_struct p,
		@@ -5917,6 +5919,9 @@ static inline int find_idlest_cpu(struct sched_domain sd, struct task_struct p
		{
		int new_cpu = prev_cpu;

		if (!cpumask_intersects(sched_domain_span(sd), &p->cpus_allowed))
		return prev_cpu;

		while (sd) {
		struct sched_group *group;
		struct sched_domain *tmp;

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