[PATCH v3 1/9] cgroup/cpuset: Inherit parent's load balance state in v2

Waiman Long
2023-06-27T00:55:21Z

Since commit f28e22441f35 ("cgroup/cpuset: Add a new isolated
cpus.partition type"), the CS_SCHED_LOAD_BALANCE bit of a v2 cpuset
can be on or off. The child cpusets of a partition root must have the
same setting as its parent or it may screw up the rebuilding of sched
domains. Fix this problem by making sure the a child v2 cpuset will
follows its parent cpuset load balance state unless the child cpuset
is a new partition root itself.

Fixes: f28e22441f35 ("cgroup/cpuset: Add a new isolated cpus.partition type")
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 58e6f18f01c1..170e342b07e3 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1588,11 +1588,16 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
}

/*
- * Skip the whole subtree if the cpumask remains the same
- * and has no partition root state and force flag not set.
+ * Skip the whole subtree if
+ * 1) the cpumask remains the same,
+ * 2) has no partition root state,
+ * 3) force flag not set, and
+ * 4) for v2 load balance state same as its parent.
*/
if (!cp->partition_root_state && !force &&
- cpumask_equal(tmp->new_cpus, cp->effective_cpus)) {
+ cpumask_equal(tmp->new_cpus, cp->effective_cpus) &&
+ (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+ (is_sched_load_balance(parent) == is_sched_load_balance(cp)))) {
pos_css = css_rightmost_descendant(pos_css);
continue;
}
@@ -1675,6 +1680,20 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,

update_tasks_cpumask(cp, tmp->new_cpus);

+ /*
+ * On default hierarchy, inherit the CS_SCHED_LOAD_BALANCE
+ * from parent if current cpuset isn't a valid partition root
+ * and their load balance states differ.
+ */
+ if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+ !is_partition_valid(cp) &&
+ (is_sched_load_balance(parent) != is_sched_load_balance(cp))) {
+ if (is_sched_load_balance(parent))
+ set_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
+ else
+ clear_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
+ }
+
/*
* On legacy hierarchy, if the effective cpumask of any non-
* empty cpuset is changed, we need to rebuild sched domains.
@@ -3222,6 +3241,14 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
cs->use_parent_ecpus = true;
parent->child_ecpus_count++;
}
+
+ /*
+ * For v2, clear CS_SCHED_LOAD_BALANCE if parent is isolated
+ */
+ if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+ !is_sched_load_balance(parent))
+ clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+
spin_unlock_irq(&callback_lock);

if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags))
--
2.31.1