[PATCH v5 3/6] cgroup/cpuset: Set isolated_cpus_updating only if isolated_cpus is changed

[Waiman Long <longman@redhat.com>]

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.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/cgroup/cpuset.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index e55855269432..c792380f9b60 100644
--- a/kernel/cgroup/cpuset.c
+++ b/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;
 }
 
-- 
2.52.0