[tip: sched/core] sched/fair: Make sure to try to detach at least one movable task

tip-bot2 for Vincent Guittot
2022-09-15T14:24:41Z

The following commit has been merged into the sched/core branch of tip:

Commit-ID: b0defa7ae03ecf91b8bfd10ede430cff12fcbd06
Gitweb: https://git.kernel.org/tip/b0defa7ae03ecf91b8bfd10ede430cff12fcbd06
Author: Vincent Guittot <vincent.guittot@linaro.org>
AuthorDate: Thu, 25 Aug 2022 14:27:23 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 15 Sep 2022 16:13:51 +02:00

sched/fair: Make sure to try to detach at least one movable task

During load balance, we try at most env->loop_max time to move a task.
But it can happen that the loop_max LRU tasks (ie tail of
the cfs_tasks list) can't be moved to dst_cpu because of affinity.
In this case, loop in the list until we found at least one.

The maximum of detached tasks remained the same as before.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220825122726.20819-2-vincent.guittot@linaro.org
---
kernel/sched/fair.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4e5b171..dae3bfa 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8049,8 +8049,12 @@ static int detach_tasks(struct lb_env *env)
p = list_last_entry(tasks, struct task_struct, se.group_node);

env->loop++;
- /* We've more or less seen every task there is, call it quits */
- if (env->loop > env->loop_max)
+ /*
+ * We've more or less seen every task there is, call it quits
+ * unless we haven't found any movable task yet.
+ */
+ if (env->loop > env->loop_max &&
+ !(env->flags & LBF_ALL_PINNED))
break;

/* take a breather every nr_migrate tasks */
@@ -10179,7 +10183,9 @@ more_balance:

if (env.flags & LBF_NEED_BREAK) {
env.flags &= ~LBF_NEED_BREAK;
- goto more_balance;
+ /* Stop if we tried all running tasks */
+ if (env.loop < busiest->nr_running)
+ goto more_balance;
}

/*