On Mon, Jun 18, 2018 at 12:14:01PM +0800, Waiman Long wrote:

+  cpuset.sched.domain_root

Why are we calling this a domain_root and not a partition?

+	A read-write single value file which exists on non-root
+	cpuset-enabled cgroups.  It is a binary value flag that accepts
+	either "0" (off) or "1" (on).  This flag is set by the parent
+	and is not delegatable.

You still haven't answered:

  https://lkml.kernel.org/r/20180531094943.GG12180@hirez.programming.kicks-ass.net

the question stands.

+	If set, it indicates that the current cgroup is the root of a
+	new scheduling domain or partition that comprises itself and
+	all its descendants except those that are scheduling domain
+	roots themselves and their descendants.  The root cgroup is
+	always a scheduling domain root.
+
+	There are constraints on where this flag can be set.  It can
+	only be set in a cgroup if all the following conditions are true.
+
+	1) The "cpuset.cpus" is not empty and the list of CPUs are
+	   exclusive, i.e. they are not shared by any of its siblings.
+	2) The "cpuset.cpus" is also a proper subset of the parent's
+	   "cpuset.cpus.effective".
+	3) The parent cgroup is a scheduling domain root.
+	4) There is no child cgroups with cpuset enabled.  This is
+	   for eliminating corner cases that have to be handled if such
+	   a condition is allowed.
+
+	Setting this flag will take the CPUs away from the effective
+	CPUs of the parent cgroup.  Once it is set, this flag cannot be
+	cleared if there are any child cgroups with cpuset enabled.
+
+	A parent scheduling domain root cgroup cannot distribute
+	all its CPUs to its child scheduling domain root cgroups.
+	There must be at least one cpu left in the parent scheduling
+	domain root cgroup.

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