----- Original Message -----
From: Waiman Long <longman@xxxxxxxxxx>
To: Tejun Heo <tj@xxxxxxxxxx>, Zefan Li <lizefan.x@xxxxxxxxxxxxx>, Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: cgroups@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Xavier <ghostxavier@xxxxxxxx>, Waiman Long <longman@xxxxxxxxxx>
Subject: [PATCH-cgroup 1/2] cgroup/cpuset: Fix remote root partition creation problem
Date: 2024-06-06 01:19
Since commit 181c8e091aae ("cgroup/cpuset: Introduce remote partition"),
a remote partition can be created underneath a non-partition root cpuset
as long as its exclusive_cpus are set to distribute exclusive CPUs down
to its children. The generate_sched_domains() function, however, doesn't
take into account this new behavior and hence will fail to create the
sched domain needed for a remote root (non-isolated) partition.
There are two issues related to remote partition support. First of
all, generate_sched_domains() has a fast path that is activated if
root_load_balance is true and top_cpuset.nr_subparts is non-zero. The
later condition isn't quite correct for remote partitions as nr_subparts
just shows the number of local child partitions underneath it. There
can be no local child partition under top_cpuset even if there are
remote partitions further down the hierarchy. Fix that by checking
for subpartitions_cpus which contains exclusive CPUs allocated to both
local and remote partitions.
Secondly, the valid partition check for subtree skipping in the csa[]
generation loop isn't enough as remote partition does not need to
have a partition root parent. Fix this problem by breaking csa[] array
generation loop of generate_sched_domains() into v1 and v2 specific parts
and checking a cpuset's exclusive_cpus before skipping its subtree in
the v2 case.
Also simplify generate_sched_domains() for cgroup v2 as only
non-isolating partition roots should be included in building the cpuset
array and none of the v1 scheduling attributes other than a different
way to create an isolated partition are supported.
Fixes: 181c8e091aae ("cgroup/cpuset: Introduce remote partition")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 55 ++++++++++++++++++++++++++++++++----------
1 file changed, 42 insertions(+), 13 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index f9b97f65e204..fb71d710a603 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -169,7 +169,7 @@ struct cpuset {
/* for custom sched domain */
int relax_domain_level;
- /* number of valid sub-partitions */
+ /* number of valid local child partitions */
int nr_subparts;
/* partition root state */
@@ -957,13 +957,14 @@ static int generate_sched_domains(cpumask_var_t **domains,
int nslot; /* next empty doms[] struct cpumask slot */
struct cgroup_subsys_state *pos_css;
bool root_load_balance = is_sched_load_balance(&top_cpuset);
+ bool cgrpv2 = cgroup_subsys_on_dfl(cpuset_cgrp_subsys);
doms = NULL;
dattr = NULL;
csa = NULL;
/* Special case for the 99% of systems with one, full, sched domain */
- if (root_load_balance && !top_cpuset.nr_subparts) {
+ if (root_load_balance && cpumask_empty(subpartitions_cpus)) {
single_root_domain:
ndoms = 1;
doms = alloc_sched_domains(ndoms);
@@ -992,16 +993,18 @@ static int generate_sched_domains(cpumask_var_t **domains,
cpuset_for_each_descendant_pre(cp, pos_css, &top_cpuset) {
if (cp == &top_cpuset)
continue;
+
+ if (cgrpv2)
+ goto v2;
+
/*
+ * v1:
* Continue traversing beyond @cp iff @cp has some CPUs and
* isn't load balancing. The former is obvious. The
* latter: All child cpusets contain a subset of the
* parent's cpus, so just skip them, and then we call
* update_domain_attr_tree() to calc relax_domain_level of
* the corresponding sched domain.
- *
- * If root is load-balancing, we can skip @cp if it
- * is a subset of the root's effective_cpus.
*/
if (!cpumask_empty(cp->cpus_allowed) &&
!(is_sched_load_balance(cp) &&
@@ -1009,16 +1012,28 @@ static int generate_sched_domains(cpumask_var_t **domains,
housekeeping_cpumask(HK_TYPE_DOMAIN))))
continue;
- if (root_load_balance &&
- cpumask_subset(cp->cpus_allowed, top_cpuset.effective_cpus))
- continue;
-
if (is_sched_load_balance(cp) &&
!cpumask_empty(cp->effective_cpus))
csa[csn++] = cp;
- /* skip @cp's subtree if not a partition root */
- if (!is_partition_valid(cp))
+ /* skip @cp's subtree */
+ pos_css = css_rightmost_descendant(pos_css);
+ continue;
+
+v2:
+ /*
+ * Only valid partition roots that are not isolated and with
+ * non-empty effective_cpus will be saved into csn[].
+ */
+ if ((cp->partition_root_state == PRS_ROOT) &&
+ !cpumask_empty(cp->effective_cpus))
+ csa[csn++] = cp;
+
+ /*
+ * Skip @cp's subtree if not a partition root and has no
+ * exclusive CPUs to be granted to child cpusets.
+ */
+ if (!is_partition_valid(cp) && cpumask_empty(cp->exclusive_cpus))
pos_css = css_rightmost_descendant(pos_css);
}
rcu_read_unlock();
@@ -1072,6 +1087,20 @@ static int generate_sched_domains(cpumask_var_t **domains,
dattr = kmalloc_array(ndoms, sizeof(struct sched_domain_attr),
GFP_KERNEL);
+ /*
+ * Cgroup v2 doesn't support domain attributes, just set all of them
+ * to SD_ATTR_INIT. Also non-isolating partition root CPUs are a
+ * subset of HK_TYPE_DOMAIN housekeeping CPUs.
+ */
+ if (cgrpv2) {
+ for (i = 0; i < ndoms; i++) {
+ cpumask_copy(doms[i], csa[i]->effective_cpus); /*****************************************/
+ if (dattr)
+ dattr[i] = SD_ATTR_INIT;
+ }
+ goto done;
+ }
+
for (nslot = 0, i = 0; i < csn; i++) {
struct cpuset *a = csa[i];
struct cpumask *dp;
@@ -1231,7 +1260,7 @@ static void rebuild_sched_domains_locked(void)
* root should be only a subset of the active CPUs. Since a CPU in any
* partition root could be offlined, all must be checked.
*/
- if (top_cpuset.nr_subparts) {
+ if (!cpumask_empty(subpartitions_cpus)) {
rcu_read_lock();
cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
if (!is_partition_valid(cs)) {
@@ -4575,7 +4604,7 @@ static void cpuset_handle_hotplug(void)
* In the rare case that hotplug removes all the cpus in
* subpartitions_cpus, we assumed that cpus are updated.
*/
- if (!cpus_updated && top_cpuset.nr_subparts)
+ if (!cpus_updated && !cpumask_empty(subpartitions_cpus))
cpus_updated = true;
/* For v1, synchronize cpus_allowed to cpu_active_mask */
--
2.39.3
