linux-kernel - [PATCH RFC v2 04/22] cpuset: introduce partition

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Message-Id: <20251025064844.495525-5-chenridong@huaweicloud.com>
Date: Sat, 25 Oct 2025 06:48:26 +0000
From: Chen Ridong <chenridong@...weicloud.com>
To: longman@...hat.com,
	tj@...nel.org,
	hannes@...xchg.org,
	mkoutny@...e.com
Cc: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	lujialin4@...wei.com,
	chenridong@...wei.com
Subject: [PATCH RFC v2 04/22] cpuset: introduce partition_enable()

From: Chen Ridong <chenridong@...wei.com>

Add partition_enable() to consolidate updates to key cpuset structures
during partition enablement, including:
- remote_sibling
- effective_xcpus
- partition_root_state
- prs_err

Key operations performed:
- Invokes partition_xcpus_add() to assign exclusive CPUs
- Maintains remote partition sibling links
- Syncs the effective_xcpus mask
- Updates partition_root_state and prs_err
- Triggers scheduler domain rebuilds
- Sends partition change notifications

This helper enables transitions between root and isolated states. All
fields except remote_sibling are reassigned during the transition.

Signed-off-by: Chen Ridong <chenridong@...wei.com>
---
 kernel/cgroup/cpuset.c | 49 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 493e094961da..c767d1be6bbb 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1521,6 +1521,55 @@ static inline bool is_local_partition(struct cpuset *cs)
 	return is_partition_valid(cs) && !is_remote_partition(cs);
 }
 
+static void partition_state_update(struct cpuset *cs, int new_prs,
+				   enum prs_errcode prs_err)
+{
+	lockdep_assert_held(&callback_lock);
+
+	cs->partition_root_state = new_prs;
+	WRITE_ONCE(cs->prs_err, prs_err);
+	if (!is_partition_valid(cs))
+		reset_partition_data(cs);
+}
+
+/**
+ * partition_enable - Transitions a cpuset to a partition root
+ * @cs: The cpuset to enable partition for
+ * @parent: Parent cpuset of @cs, NULL for remote parent
+ * @new_prs: New partition state to set
+ * @new_excpus: New effective exclusive CPUs mask for the partition
+ *
+ * Transitions a cpuset to a partition root, only for v2.
+ * It supports the transition between root and isolated partition.
+ */
+static void partition_enable(struct cpuset *cs, struct cpuset *parent,
+			     int new_prs, struct cpumask *new_excpus)
+{
+	bool isolcpus_updated;
+	int old_prs;
+
+	lockdep_assert_held(&cpuset_mutex);
+	WARN_ON_ONCE(new_prs <= 0);
+	WARN_ON_ONCE(!cpuset_v2());
+
+	if (cs->partition_root_state == new_prs)
+		return;
+
+	old_prs = cs->partition_root_state;
+	spin_lock_irq(&callback_lock);
+	/* enable partition should only add exclusive cpus */
+	isolcpus_updated = partition_xcpus_add(new_prs, parent, new_excpus);
+	/* enable remote partition */
+	if (!parent && list_empty(&cs->remote_sibling))
+		list_add(&cs->remote_sibling, &remote_children);
+	cpumask_copy(cs->effective_xcpus, new_excpus);
+	partition_state_update(cs, new_prs, PERR_NONE);
+	spin_unlock_irq(&callback_lock);
+	update_unbound_workqueue_cpumask(isolcpus_updated);
+	cpuset_force_rebuild();
+	notify_partition_change(cs, old_prs);
+}
+
 /*
  * prstate_housekeeping_conflict - check for partition & housekeeping conflicts
  * @prstate: partition root state to be checked
-- 
2.34.1