[PATCH v3 1/2] docs: cgroup-v2: Describe boot-isolated CPUs in cpuset.cpus.isolated

[Guopeng Zhang <guopeng.zhang@linux.dev>]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

cpuset.cpus.isolated is documented as empty when no isolated partition
exists. This is not true when CPUs are isolated at boot with
isolcpus=domain. cpuset_init() adds those CPUs to the isolated mask,
and isolcpus=<cpu-list> uses domain isolation by default. They remain
listed after a partition using them is released.

Document the boot-isolated CPUs as well.

Suggested-by: Ridong Chen <ridong.chen@linux.dev>
Reviewed-by: Ridong Chen <ridong.chen@linux.dev>
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 Documentation/admin-guide/cgroup-v2.rst | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 2ec582985b5b..18a01ce4c334 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2626,8 +2626,9 @@ Cpuset Interface Files
 	A read-only and root cgroup only multiple values file.
 
 	This file shows the set of all isolated CPUs used in existing
-	isolated partitions. It will be empty if no isolated partition
-	is created.
+	isolated partitions or isolated at boot time via the "domain"
+	flag of "isolcpus". The latter remain listed even after any
+	partition using them is released.
 
   cpuset.cpus.partition
 	A read-write single value file which exists on non-root
-- 
2.43.0