sched/deadline: Avoid pointless __setscheduler()

There is no need to dequeue/enqueue and push/pull if there are
no scheduling parameters changed for the DL class.

Both fair and RT classes already check if parameters changed for
them to avoid unnecessary overhead. This patch add the parameters
changed test for the DL class in order to reduce overhead.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
[ Fixed up the changelog. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Kirill Tkhai <ktkhai@parallels.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1416962647-76792-5-git-send-email-wanpeng.li@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 50a5352f620507cb4b440a58dd83e35932fa16f9..d59652d60f86cf983c9a263a91600ff5879001a1 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3417,6 +3417,20 @@ static bool check_same_owner(struct task_struct *p)
        return match;
 }
 
+static bool dl_param_changed(struct task_struct *p,
+               const struct sched_attr *attr)
+{
+       struct sched_dl_entity *dl_se = &p->dl;
+
+       if (dl_se->dl_runtime != attr->sched_runtime ||
+               dl_se->dl_deadline != attr->sched_deadline ||
+               dl_se->dl_period != attr->sched_period ||
+               dl_se->flags != attr->sched_flags)
+               return true;
+
+       return false;
+}
+
 static int __sched_setscheduler(struct task_struct *p,
                                const struct sched_attr *attr,
                                bool user)
@@ -3545,7 +3559,7 @@ recheck:
                        goto change;
                if (rt_policy(policy) && attr->sched_priority != p->rt_priority)
                        goto change;
-               if (dl_policy(policy))
+               if (dl_policy(policy) && dl_param_changed(p, attr))
                        goto change;
 
                p->sched_reset_on_fork = reset_on_fork;