Messages in this thread Patch in this message | | | Date | Tue, 10 Oct 2017 04:00:39 -0700 | From | tip-bot for Brendan Jackman <> | Subject | [tip:sched/core] sched/fair: Fix usage of find_idlest_group() when no groups are allowed |
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Commit-ID: 6fee85ccbc76e8aeba43dc120c5fa3c5409a4e2c Gitweb: https://git.kernel.org/tip/6fee85ccbc76e8aeba43dc120c5fa3c5409a4e2c Author: Brendan Jackman <brendan.jackman@arm.com> AuthorDate: Thu, 5 Oct 2017 12:45:15 +0100 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 10 Oct 2017 11:45:35 +0200
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> --- kernel/sched/fair.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index cca1835..ed80d6b 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -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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