sched: Avoid going ahead if ->cpus_allowed is not changed

If cpumask_equal(&p->cpus_allowed, new_mask) is true, seems
there is no reason to prevent set_cpus_allowed_ptr() return
directly.
Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
Acked-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110509140705.GA2219@zhySigned-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -5946,13 +5946,15 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 
 	rq = task_rq_lock(p, &flags);
 
+	if (cpumask_equal(&p->cpus_allowed, new_mask))
+		goto out;
+
 	if (!cpumask_intersects(new_mask, cpu_active_mask)) {
 		ret = -EINVAL;
 		goto out;
 	}
 
-	if (unlikely((p->flags & PF_THREAD_BOUND) && p != current &&
-		     !cpumask_equal(&p->cpus_allowed, new_mask))) {
+	if (unlikely((p->flags & PF_THREAD_BOUND) && p != current)) {
 		ret = -EINVAL;
 		goto out;
 	}