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Subject[PATCH] sched/core: Reduce cost of sched_move_task when config autogroup
Date
Some sched_move_task calls of autogroup is useless when the
task_struct->sched_task_group isn't changed because of task_group
of cpu_cgroup overlay task_group of autogroup. The overlay key codes
are as follows:

sched_cgroup_fork->autogroup_task_group->task_wants_autogroup
sched_change_group->autogroup_task_group->autogroup_task_group

sched_move_task eg:
task A belongs to cpu_cgroup0 and autogroup0, it will always to
cpu_cgroup0 when doing exit. So there is no need to do {de|en}queue.
The call graph is as follow.

do_exit
sched_autogroup_exit_task
sched_move_task
dequeue_task
sched_change_group
A.sched_task_group = sched_get_task_group
enqueue_task

So do some check before dequeue task in sched_move_task.

Signed-off-by: wuchi <wuchi.zero@gmail.com>
---
kernel/sched/core.c | 29 +++++++++++++++++++++++++++--
1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index a380f34789a2..acc9a0e391f4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10330,7 +10330,7 @@ void sched_release_group(struct task_group *tg)
spin_unlock_irqrestore(&task_group_lock, flags);
}

-static void sched_change_group(struct task_struct *tsk)
+static struct task_group *sched_get_task_group(struct task_struct *tsk)
{
struct task_group *tg;

@@ -10342,7 +10342,28 @@ static void sched_change_group(struct task_struct *tsk)
tg = container_of(task_css_check(tsk, cpu_cgrp_id, true),
struct task_group, css);
tg = autogroup_task_group(tsk, tg);
- tsk->sched_task_group = tg;
+
+ return tg;
+}
+
+static bool sched_task_group_changed(struct task_struct *tsk)
+{
+ /*
+ * Some sched_move_task calls of autogroup is useless when the
+ * task_struct->sched_task_group isn't changed because of task_group
+ * of cpu_cgroup overlay task_group of autogroup. so do some check
+ * before dequeue task in sched_move_task.
+ */
+#ifdef CONFIG_SCHED_AUTOGROUP
+ return sched_get_task_group(tsk) != tsk->sched_task_group;
+#else
+ return true;
+#endif /* CONFIG_SCHED_AUTOGROUP */
+}
+
+static void sched_change_group(struct task_struct *tsk)
+{
+ tsk->sched_task_group = sched_get_task_group(tsk);

#ifdef CONFIG_FAIR_GROUP_SCHED
if (tsk->sched_class->task_change_group)
@@ -10369,6 +10390,9 @@ void sched_move_task(struct task_struct *tsk)
rq = task_rq_lock(tsk, &rf);
update_rq_clock(rq);

+ if (!sched_task_group_changed(tsk))
+ goto unlock;
+
running = task_current(rq, tsk);
queued = task_on_rq_queued(tsk);

@@ -10391,6 +10415,7 @@ void sched_move_task(struct task_struct *tsk)
resched_curr(rq);
}

+unlock:
task_rq_unlock(rq, tsk, &rf);
}

--
2.20.1
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