[tip: sched/core] sched/fair: Better document newidle_balance()

[tip-bot2 for Peter Zijlstra]

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

Commit-ID:     7277a34c6be0b2972bdd1fea88c7cef409bed5b4
Gitweb:        https://git.kernel.org/tip/7277a34c6be0b2972bdd1fea88c7cef409bed5b4
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Fri, 08 Nov 2019 14:15:55 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Mon, 11 Nov 2019 08:35:18 +01:00

sched/fair: Better document newidle_balance()

Whilst chasing the pick_next_task() race, there was some confusion
about the newidle_balance() return values. Document them.

[ mingo: Minor edits. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bsegall@xxxxxxxxxx
Cc: dietmar.eggemann@xxxxxxx
Cc: juri.lelli@xxxxxxxxxx
Cc: ktkhai@xxxxxxxxxxxxx
Cc: mgorman@xxxxxxx
Cc: qais.yousef@xxxxxxx
Cc: qperret@xxxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
Cc: valentin.schneider@xxxxxxx
Cc: vincent.guittot@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20191108131909.488364308@xxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 kernel/sched/fair.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6e622f4..c48a695 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9941,6 +9941,11 @@ static inline void nohz_newidle_balance(struct rq *this_rq) { }
 /*
  * idle_balance is called by schedule() if this_cpu is about to become
  * idle. Attempts to pull tasks from other CPUs.
+ *
+ * Returns:
+ *   < 0 - we released the lock and there are !fair tasks present
+ *     0 - failed, no new tasks
+ *   > 0 - success, new (fair) tasks present
  */
 int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 {