[PATCH v3 4/9] cgroup/cpuset: Allow suppression of sched domain rebuild in update_cpumasks_hier()

Waiman Long
2023-06-27T00:55:24Z

A single partition setup and tear-down operation can lead to
multiple rebuild_sched_domains_locked() calls which is a waste of
effort. This can partly be mitigated by adding a flag to suppress the
rebuild_sched_domains_locked() call in update_cpumasks_hier(). Since
a Boolean flag has already been passed as the 3rd argument to
update_cpumasks_hier(), we can extend that to a full flag word.

The sched domain rebuild suppression is now enabled in
update_sibling_cpumasks() as all it callers will do the sched domain
rebuild after its return later on anyway.

Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index b8ccc1be7bde..64f9e305b3ab 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1590,6 +1590,12 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
return 0;
}

+/*
+ * update_cpumasks_hier() flags
+ */
+#define HIER_CHECKALL 0x01 /* Check all cpusets with no skipping */
+#define HIER_NO_SD_REBUILD 0x02 /* Don't rebuild sched domains */
+
/*
* update_cpumasks_hier - Update effective cpumasks and tasks in the subtree
* @cs: the cpuset to consider
@@ -1604,7 +1610,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cs, int cmd,
* Called with cpuset_mutex held
*/
static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
- bool force)
+ int flags)
{
struct cpuset *cp;
struct cgroup_subsys_state *pos_css;
@@ -1644,10 +1650,10 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
* Skip the whole subtree if
* 1) the cpumask remains the same,
* 2) has no partition root state,
- * 3) force flag not set, and
+ * 3) HIER_CHECKALL flag not set, and
* 4) for v2 load balance state same as its parent.
*/
- if (!cp->partition_root_state && !force &&
+ if (!cp->partition_root_state && !(flags & HIER_CHECKALL) &&
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)))) {
@@ -1764,7 +1770,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
}
rcu_read_unlock();

- if (need_rebuild_sched_domains)
+ if (need_rebuild_sched_domains && !(flags & HIER_NO_SD_REBUILD))
rebuild_sched_domains_locked();
}

@@ -1788,7 +1794,9 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
* to use the right effective_cpus value.
*
* The update_cpumasks_hier() function may sleep. So we have to
- * release the RCU read lock before calling it.
+ * release the RCU read lock before calling it. HIER_NO_SD_REBUILD
+ * flag is used to suppress rebuild of sched domains as the callers
+ * will take care of that.
*/
rcu_read_lock();
cpuset_for_each_child(sibling, pos_css, parent) {
@@ -1800,7 +1808,7 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
continue;

rcu_read_unlock();
- update_cpumasks_hier(sibling, tmp, false);
+ update_cpumasks_hier(sibling, tmp, HIER_NO_SD_REBUILD);
rcu_read_lock();
css_put(&sibling->css);
}
@@ -1913,7 +1921,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
spin_unlock_irq(&callback_lock);

/* effective_cpus will be updated here */
- update_cpumasks_hier(cs, &tmp, false);
+ update_cpumasks_hier(cs, &tmp, 0);

if (cs->partition_root_state) {
struct cpuset *parent = parent_cs(cs);
@@ -2382,7 +2390,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
* Force update if switching back to member.
*/
if (!list_empty(&cs->css.children))
- update_cpumasks_hier(cs, &tmpmask, !new_prs);
+ update_cpumasks_hier(cs, &tmpmask, !new_prs ? HIER_CHECKALL : 0);

/* Update sched domains and load balance flag */
update_partition_sd_lb(cs, old_prs);
--
2.31.1