From: Vincent Donnefort vincent.donnefort@arm.com
[ Upstream commit 014ba44e8184e1acf93e0cbb7089ee847802f8f0 ]
select_idle_sibling() has a special case for tasks woken up by a per-CPU kthread where the selected CPU is the previous one. For asymmetric CPU capacity systems, the assumption was that the wakee couldn't have a bigger utilization during task placement than it used to have during the last activation. That was not considering uclamp.min which can completely change between two task activations and as a consequence mandates the fitness criterion asym_fits_capacity(), even for the exit path described above.
Fixes: b4c9c9f15649 ("sched/fair: Prefer prev cpu in asymmetric wakeup path") Signed-off-by: Vincent Donnefort vincent.donnefort@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Valentin Schneider valentin.schneider@arm.com Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com Link: https://lkml.kernel.org/r/20211129173115.4006346-1-vincent.donnefort@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a7589552be5fc..2a33cb5a10e59 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6286,7 +6286,8 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) if (is_per_cpu_kthread(current) && in_task() && prev == smp_processor_id() && - this_rq()->nr_running <= 1) { + this_rq()->nr_running <= 1 && + asym_fits_capacity(task_util, prev)) { return prev; }