cgroup/cpuset: Set isolated_cpus_updating only if isolated_cpus is changed

As cpuset is updating HK_TYPE_DOMAIN housekeeping mask when there is
a change in the set of isolated CPUs, making this change is now more
costly than before.  Right now, the isolated_cpus_updating flag can be
set even if there is no real change in isolated_cpus. Put in additional
checks to make sure that isolated_cpus_updating is set only if there
is a real change in isolated_cpus.

Reviewed-by: Chen Ridong <[email protected]>
Signed-off-by: Waiman Long <[email protected]>
Signed-off-by: Tejun Heo <[email protected]>

Author: Waiman-Long

kernel/cgroup/cpuset.c

@@ -1180,11 +1180,15 @@ static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus
 	WARN_ON_ONCE(old_prs == new_prs);
 	lockdep_assert_held(&callback_lock);
 	lockdep_assert_held(&cpuset_mutex);
-	if (new_prs == PRS_ISOLATED)
+	if (new_prs == PRS_ISOLATED) {
+		if (cpumask_subset(xcpus, isolated_cpus))
+			return;
 		cpumask_or(isolated_cpus, isolated_cpus, xcpus);
-	else
+	} else {
+		if (!cpumask_intersects(xcpus, isolated_cpus))
+			return;
 		cpumask_andnot(isolated_cpus, isolated_cpus, xcpus);
-
+	}
 	isolated_cpus_updating = true;
 }