Re: [PATCH RFC v2 10/22] cpuset: introduce local_partition_enable()
From: Waiman Long
Date: Wed Nov 12 2025 - 21:58:13 EST
On 11/12/25 9:49 PM, Chen Ridong wrote:
On 2025/11/13 5:47, Waiman Long wrote:
On 10/25/25 2:48 AM, Chen Ridong wrote:I want to support switching the root partition’s state between "root" and "isolated"—for example, an
From: Chen Ridong <chenridong@xxxxxxxxxx>What is the purpose of this cpumask_andnot() operation? Is it just to create the cpumask_updated
The partition_enable() function introduced in the previous patch can be
reused to enable local partitions.
The local_partition_enable() function is introduced, which factors out the
local partition enablement logic from update_parent_effective_cpumask().
After passing local partition validation checks, it delegates to
partition_enable() to complete the partition setup.
This refactoring creates a clear separation between local and remote
partition operations while maintaining code reuse through the shared
partition_enable() infrastructure.
Signed-off-by: Chen Ridong <chenridong@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 94 ++++++++++++++++++++++++++----------------
1 file changed, 59 insertions(+), 35 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 5b57c5370641..b308d9f80eef 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1822,6 +1822,61 @@ static void remote_cpus_update(struct cpuset *cs, struct cpumask *xcpus,
remote_partition_disable(cs, tmp);
}
+/**
+ * local_partition_enable - Enable local partition for a cpuset
+ * @cs: Target cpuset to become a local partition root
+ * @new_prs: New partition root state to apply
+ * @tmp: Temporary masks for CPU calculations
+ *
+ * This function enables local partition root capability for a cpuset by
+ * validating prerequisites, computing exclusive CPUs, and updating the
+ * partition hierarchy.
+ *
+ * Return: 0 on success, error code on failure
+ */
+static int local_partition_enable(struct cpuset *cs,
+ int new_prs, struct tmpmasks *tmp)
+{
+ struct cpuset *parent = parent_cs(cs);
+ enum prs_errcode part_error;
+ bool cpumask_updated = false;
+
+ lockdep_assert_held(&cpuset_mutex);
+ WARN_ON_ONCE(is_remote_partition(cs)); /* For local partition only */
+
+ /*
+ * The parent must be a partition root.
+ * The new cpumask, if present, or the current cpus_allowed must
+ * not be empty.
+ */
+ if (!is_partition_valid(parent)) {
+ return is_partition_invalid(parent)
+ ? PERR_INVPARENT : PERR_NOTPART;
+ }
+
+ /*
+ * Need to call compute_excpus() in case
+ * exclusive_cpus not set. Sibling conflict should only happen
+ * if exclusive_cpus isn't set.
+ */
+ if (compute_excpus(cs, tmp->new_cpus))
+ WARN_ON_ONCE(!cpumask_empty(cs->exclusive_cpus));
+
+ part_error = validate_partition(cs, new_prs, tmp->new_cpus);
+ if (part_error)
+ return part_error;
+
+ cpumask_updated = cpumask_andnot(tmp->addmask, tmp->new_cpus,
+ parent->effective_cpus);
boolean? At this point, cpumask_updated should always be true. If not, we have to add validation
check to return an error.
Cheers,
Longman
isolated partition switching to root without changing its CPU mask.
Adding a comment to clarify this behavior would be helpful.
For state switching, I would suggest to use a separate helper just for state switching as such switching can be done to both local and remote partition.
Cheers,
Longman