As reported by sashiko [1], cpuset_hotplug_update_tasks() may perform
unnecessary task iteration and updating of tasks' CPU and node masks
when mems_allowed and/or cpus_allowed are not set in cpuset v2. It is
due to the fact that the temporary new_cpus and new_mems masks do not
inherit parent's effective_cpus/mems when they are empty which is the
expected behavior for cpuset v2 since commit 4ec22e9c5a90 ("cpuset:
Enable cpuset controller in default hierarchy").Fix that and avoid unnecessay work by enhancing compute_effective_cpumask() to add the empty cpumask check and inheriting the parent's versions if empty when in v2. A new compute_effective_nodemask() helper is also added to perform similar function for new effective_mems. Add new test_cpuset_prs.sh test cases to confirm that effective_cpus will inherit the parent's version if cpuset.cpus is empty. [1] https://sashiko.dev/#/patchset/20260621032816.1806773-1-longman%40redhat.com Suggested-by: Ridong Chen <[email protected]> Fixes: 4ec22e9c5a90 ("cpuset: Enable cpuset controller in default hierarchy") Signed-off-by: Waiman Long <[email protected]> --- kernel/cgroup/cpuset.c | 45 +++++++++++-------- .../selftests/cgroup/test_cpuset_prs.sh | 11 ++++- 2 files changed, 35 insertions(+), 21 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index aff86acea701..044ddbf66f8e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1094,12 +1094,35 @@ void cpuset_update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus) * @cs: the cpuset the need to recompute the new effective_cpus mask * @parent: the parent cpuset * + * For v2, the parent's effective_cpus is inherited if cpumask empty. * The result is valid only if the given cpuset isn't a partition root. */ static void compute_effective_cpumask(struct cpumask *new_cpus, struct cpuset *cs, struct cpuset *parent) { - cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus); + bool has_cpus; + + has_cpus = cpumask_and(new_cpus, cs->cpus_allowed, parent->effective_cpus); + if (!has_cpus && is_in_v2_mode()) + cpumask_copy(new_cpus, parent->effective_cpus); +} + +/** + * compute_effective_nodemask - Compute the effective nodemask of the cpuset + * @new_cpus: the temp variable for the new effective_mems mask + * @cs: the cpuset the need to recompute the new effective_mems mask + * @parent: the parent cpuset + * + * For v2, the parent's effective_mems is inherited if nodemask empty. + */ +static void compute_effective_nodemask(nodemask_t *new_mems, + struct cpuset *cs, struct cpuset *parent) +{ + bool has_mems; + + has_mems = nodes_and(*new_mems, cs->mems_allowed, parent->effective_mems); + if (!has_mems && is_in_v2_mode()) + nodes_copy(*new_mems, parent->effective_mems); } /* @@ -2148,15 +2171,6 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, goto update_parent_effective; } - /* - * If it becomes empty, inherit the effective mask of the - * parent, which is guaranteed to have some CPUs unless - * it is a partition root that has explicitly distributed - * out all its CPUs. - */ - if (is_in_v2_mode() && !remote && cpumask_empty(tmp->new_cpus)) - cpumask_copy(tmp->new_cpus, parent->effective_cpus); - /* * Skip the whole subtree if * 1) the cpumask remains the same, @@ -2704,14 +2718,7 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems) cpuset_for_each_descendant_pre(cp, pos_css, cs) { struct cpuset *parent = parent_cs(cp); - bool has_mems = nodes_and(*new_mems, cp->mems_allowed, parent->effective_mems); - - /* - * If it becomes empty, inherit the effective mask of the - * parent, which is guaranteed to have some MEMs. - */ - if (is_in_v2_mode() && !has_mems) - *new_mems = parent->effective_mems; + compute_effective_nodemask(new_mems, cp, parent); /* Skip the whole subtree if the nodemask remains the same. */ if (nodes_equal(*new_mems, cp->effective_mems)) { @@ -3923,7 +3930,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) parent = parent_cs(cs); compute_effective_cpumask(&new_cpus, cs, parent); - nodes_and(new_mems, cs->mems_allowed, parent->effective_mems); + compute_effective_nodemask(&new_mems, cs, parent); if (!tmp || !cs->partition_root_state) goto update_tasks; diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh index 0d41aa0d343d..ca9bc38fdb95 100755 --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh @@ -495,13 +495,20 @@ REMOTE_TEST_MATRIX=( # Narrowing cpuset.cpus to previously sibling-excluded CPUs should # not return CPUs that were never actually owned. " C1-4:P1 . C1-2:P1 C1-3:P2 . . \ - . . . C3 . . p1:4|c11:1-2|c12:3 \ + . . . C3 . . p1:4|c11:1-2|c12:3 \ p1:P1|c11:P1|c12:P2 3" # Expanding cpuset.cpus to include a previously sibling-excluded CPU # after the sibling has become a member should correctly request it. " C1-4:P1 . C1-2:P1 C1-3:P2 . . \ - . . P0 C2-3 . . p1:1,4|c11:1|c12:2-3 \ + . . P0 C2-3 . . p1:1,4|c11:1|c12:2-3 \ p1:P1|c11:P0|c12:P2 2-3" + # Cpusets with empty cpuset.cpus should inherit parent's effective_cpus + " C1-4:P1 C5-6 C1-2 . C5 . \ + . P1 P1 . . . p1:3-4|p2:5-6|c11:1-2|c12:3-4|c21:5|c22:5-6 \ + p1:P1|p2:P1|c11:P1" + " C1-4:P1 C5-6 C1-2 . C5 . \ + . P1 P1 . O5=0 . p1:3-4|p2:6|c11:1-2|c12:3-4|c21:6|c22:6 \ + p1:P1|p2:P1|c11:P1" ) # -- 2.54.0
