[PATCH] sched_deadline, docs: add affinity setting with cgroup2 cpuset controller

[Shashank Balaji <shashank.mahadasyam@sony.com>]

Setting the cpu affinity mask of a SCHED_DEADLINE process using the cgroup v1
cpuset controller is already detailed. Add similar information for cgroup v2's
cpuset controller.

Signed-off-by: Shashank Balaji <shashank.mahadasyam@sony.com>
---
 Documentation/scheduler/sched-deadline.rst | 29 +++++++++++++++++++++++------
 1 file changed, 23 insertions(+), 6 deletions(-)

diff --git a/Documentation/scheduler/sched-deadline.rst b/Documentation/scheduler/sched-deadline.rst
index a727827b8dd52710f880c2b92d3a8224c259873c..e3d7968ff6c3c43f87e249dbcb309619dbd616bf 100644
--- a/Documentation/scheduler/sched-deadline.rst
+++ b/Documentation/scheduler/sched-deadline.rst
@@ -20,7 +20,8 @@ Deadline Task Scheduling
       4.3 Default behavior
       4.4 Behavior of sched_yield()
     5. Tasks CPU affinity
-      5.1 SCHED_DEADLINE and cpusets HOWTO
+      5.1 Using cgroup v1 cpuset controller
+      5.2 Using cgroup v2 cpuset controller
     6. Future plans
     A. Test suite
     B. Minimal main()
@@ -671,12 +672,15 @@ Deadline Task Scheduling
 5. Tasks CPU affinity
 =====================
 
- -deadline tasks cannot have an affinity mask smaller that the entire
- root_domain they are created on. However, affinities can be specified
- through the cpuset facility (Documentation/admin-guide/cgroup-v1/cpusets.rst).
+ Deadline tasks cannot have a cpu affinity mask smaller than the root domain they
+ are created on. So, using ``sched_setaffinity(2)`` won't work. Instead, the
+ the deadline task should be created in a restricted root domain. This can be
+ done using the cpuset controller of either cgroup v1 (deprecated) or cgroup v2.
+ See :ref:`Documentation/admin-guide/cgroup-v1/cpusets.rst <cpusets>` and
+ :ref:`Documentation/admin-guide/cgroup-v2.rst <cgroup-v2>` for more information.
 
-5.1 SCHED_DEADLINE and cpusets HOWTO
-------------------------------------
+5.1 Using cgroup v1 cpuset controller
+-------------------------------------
 
  An example of a simple configuration (pin a -deadline task to CPU0)
  follows (rt-app is used to create a -deadline task)::
@@ -695,6 +699,19 @@ Deadline Task Scheduling
    rt-app -t 100000:10000:d:0 -D5 # it is now actually superfluous to specify
 				  # task affinity
 
+5.2 Using cgroup v2 cpuset controller
+-------------------------------------
+
+ Assuming the cgroup v2 root is mounted at ``/sys/fs/cgroup``.
+
+   cd /sys/fs/cgroup
+   echo '+cpuset' > cgroup.subtree_control
+   mkdir deadline_group
+   echo 0 > deadline_group/cpuset.cpus
+   echo 'root' > deadline_group/cpuset.cpus.partition
+   echo $$ > deadline_group/cgroup.procs
+   rt-app -t 100000:10000:d:0 -D5
+
 6. Future plans
 ===============
 

---
base-commit: a5806cd506af5a7c19bcd596e4708b5c464bfd21
change-id: 20250522-sched-deadline-cpu-affinity-b0b4edf0ddc9

Best regards,
-- 
Shashank Balaji <shashank.mahadasyam@sony.com>