linux-kernel - [PATCH 2/2] cgroup, docs: Document interaction of RT processes with cpu controller

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Message-Id: <20250305-rt-and-cpu-controller-doc-v1-2-7b6a6f5ff43d@sony.com>
Date: Wed, 05 Mar 2025 13:12:44 +0900
From: Shashank Balaji via B4 Relay <devnull+shashank.mahadasyam.sony.com@...nel.org>
To: Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
 Michal Koutný <mkoutny@...e.com>, 
 Jonathan Corbet <corbet@....net>
Cc: Waiman Long <longman@...hat.com>, cgroups@...r.kernel.org, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Shinya Takumi <shinya.takumi@...y.com>, 
 Shashank Balaji <shashank.mahadasyam@...y.com>
Subject: [PATCH 2/2] cgroup, docs: Document interaction of RT processes
 with cpu controller

From: Shashank Balaji <shashank.mahadasyam@...y.com>

If the cpu controller is enabled in a CONFIG_RT_GROUP_SCHED
disabled setting, cpu.stat and cpu.pressure account for realtime
processes, and cpu.uclamp.{min, max} affect realtime processes as well.
None of the other interface files are affected by or affect realtime
processes.

Signed-off-by: Shashank Balaji <shashank.mahadasyam@...y.com>
---
 Documentation/admin-guide/cgroup-v2.rst | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index f293a13b42ed69e7c6bf5e974cb86e228411af4e..2c267f42e5fef9c4e2c3530ce73330d680b9b2dc 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1095,7 +1095,9 @@ realtime processes irrespective of CONFIG_RT_GROUP_SCHED.
 CPU Interface Files
 ~~~~~~~~~~~~~~~~~~~
 
-All time durations are in microseconds.
+All time durations are in microseconds. Only cpu.stat and cpu.pressure account
+for realtime processes, and only cpu.uclamp.min and cpu.uclamp.max
+affect realtime processes.
 
   cpu.stat
 	A read-only flat-keyed file.
@@ -1115,6 +1117,9 @@ All time durations are in microseconds.
 	- nr_bursts
 	- burst_usec
 
+    The runtime of realtime processes is accounted for only by the usage_usec,
+	user_usec, and system_usec fields.
+
   cpu.weight
 	A read-write single value file which exists on non-root
 	cgroups.  The default is "100".
@@ -1158,8 +1163,9 @@ All time durations are in microseconds.
   cpu.pressure
 	A read-write nested-keyed file.
 
-	Shows pressure stall information for CPU. See
-	:ref:`Documentation/accounting/psi.rst <psi>` for details.
+	Shows pressure stall information for CPU, including the contribution of
+	realtime processes. See :ref:`Documentation/accounting/psi.rst <psi>`
+	for details.
 
   cpu.uclamp.min
         A read-write single value file which exists on non-root cgroups.
@@ -1170,7 +1176,8 @@ All time durations are in microseconds.
 
         This interface allows reading and setting minimum utilization clamp
         values similar to the sched_setattr(2). This minimum utilization
-        value is used to clamp the task specific minimum utilization clamp.
+        value is used to clamp the task specific minimum utilization clamp,
+        including those of realtime processes.
 
         The requested minimum utilization (protection) is always capped by
         the current value for the maximum utilization (limit), i.e.
@@ -1185,7 +1192,8 @@ All time durations are in microseconds.
 
         This interface allows reading and setting maximum utilization clamp
         values similar to the sched_setattr(2). This maximum utilization
-        value is used to clamp the task specific maximum utilization clamp.
+        value is used to clamp the task specific maximum utilization clamp,
+        including those of realtime processes.
 
   cpu.idle
 	A read-write single value file which exists on non-root cgroups.

-- 
2.43.0