linux-kernel - [PATCH v2] sched: Remove unlikely annotation from sched_move

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Date:   Mon, 6 Feb 2017 11:04:26 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH v2] sched: Remove unlikely annotation from sched_move_task()
 running check

From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>

The check for running in sched_move_task() has an unlikely() around it. That
is, it is unlikely that the task being moved is running. That use to be
true. But with a couple of recent updates, it is now likely that the task
will be running.

The first change came from ea86cb4b7621 ("sched/cgroup: Fix
cpu_cgroup_fork() handling") that moved around the use case of
sched_move_task() in do_fork() where the call is now done after the task is
woken (hence it is running).

The second change came from 8e5bfa8c1f84 ("sched/autogroup: Do not use
autogroup->tg in zombie threads") where sched_move_task() is called by the
exit path, by the task that is exiting. Hence it too is running.

Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
Changes from v1.

 Removed annotation entirely, instead of inversing it.

 Changed the subject from:

  sched: Update unlikely to now likely in sched_move_task()

 kernel/sched/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c56fb57..dbb295f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7989,14 +7989,14 @@ void sched_move_task(struct task_struct *tsk)

 	if (queued)
 		dequeue_task(rq, tsk, DEQUEUE_SAVE | DEQUEUE_MOVE);
-	if (unlikely(running))
+	if (running)
 		put_prev_task(rq, tsk);

 	sched_change_group(tsk, TASK_MOVE_GROUP);

 	if (queued)
 		enqueue_task(rq, tsk, ENQUEUE_RESTORE | ENQUEUE_MOVE);
-	if (unlikely(running))
+	if (running)
 		set_curr_task(rq, tsk);

 	task_rq_unlock(rq, tsk, &rf);
-- 
2.9.3