[PATCH] cgroup/cpu: document cpu.stat nice_usec and core_sched.force_idle_usec

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

cgroup_base_stat_cputime_show() unconditionally prints a fourth base
stat, nice_usec, in addition to usage_usec/user_usec/system_usec, and
also prints core_sched.force_idle_usec when CONFIG_SCHED_CORE is enabled.
Neither field is currently described in the cpu.stat section of
cgroup-v2.rst, which still states it "always reports the following three
stats".

nice_usec was added by commit aefa398d93d5 ("cgroup/rstat: Tracking
cgroup-level niced CPU time") and core_sched.force_idle_usec by commit
1fcf54deb767 ("sched/core: add forced idle accounting for cgroups"); the
documentation was not updated in either case.

Update the cpu.stat description to list both fields and fix the count.

Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 Documentation/admin-guide/cgroup-v2.rst | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 0df15a672cf3..778b759dd892 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1144,12 +1144,18 @@ will be referred to. All time durations are in microseconds.
 	A read-only flat-keyed file.
 	This file exists whether the controller is enabled or not.
 
-	It always reports the following three stats, which account for all the
+	It always reports the following four stats, which account for all the
 	processes in the cgroup (including those in descendant cgroups):
 
 	- usage_usec
 	- user_usec
 	- system_usec
+	- nice_usec
+
+	When core scheduling (CONFIG_SCHED_CORE) is enabled, an additional
+	stat is reported:
+
+	- core_sched.force_idle_usec
 
 	and the following five when the controller is enabled, which account for
 	only the processes under the fair-class scheduler:
-- 
2.43.0