From: Waiman Long <longman@redhat.com>
To: Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>
Cc: cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-doc@vger.kernel.org, kernel-team@fb.com, pjt@google.com,
luto@amacapital.net, Mike Galbraith <efault@gmx.de>,
torvalds@linux-foundation.org, Roman Gushchin <guro@fb.com>,
Juri Lelli <juri.lelli@redhat.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Tom Hromatka <tom.hromatka@oracle.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH v15 11/12] cpuset: Add documentation about the new "cpuset.sched.partition" flag
Date: Thu, 8 Nov 2018 10:08:45 -0500 [thread overview]
Message-ID: <1541689726-20088-12-git-send-email-longman@redhat.com> (raw)
In-Reply-To: <1541689726-20088-1-git-send-email-longman@redhat.com>
The cgroup-v2.rst file is updated to document the purpose of the new
"cpuset.sched.partition" flag and how its usage.
Signed-off-by: Waiman Long <longman@redhat.com>
---
Documentation/admin-guide/cgroup-v2.rst | 73 +++++++++++++++++++++++++++++++++
1 file changed, 73 insertions(+)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 595b075..f83a523 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -1708,6 +1708,79 @@ Cpuset Interface Files
Its value will be affected by memory nodes hotplug events.
+ cpuset.sched.partition
+ A read-write single value file which exists on non-root
+ cpuset-enabled cgroups. This flag is owned by the parent cgroup
+ and is not delegatable.
+
+ It accepts only the following input values when written to.
+
+ "root" or "1" - a paritition root
+ "member" or "0" - a non-root member of a partition
+
+ When set to be a partition root, the current cgroup is the
+ root of a new partition or scheduling domain that comprises
+ itself and all its descendants except those that are separate
+ partition roots themselves and their descendants. The root
+ cgroup is always a partition root.
+
+ There are constraints on where a partition root 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 parent cgroup is a partition root.
+ 3) The "cpuset.cpus" is also a proper subset of the parent's
+ "cpuset.cpus.effective".
+ 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 it to partition root will take the CPUs away from the
+ effective CPUs of the parent cgroup. Once it is set, this
+ file cannot be reverted back to "member" if there are any child
+ cgroups with cpuset enabled.
+
+ A parent partition cannot distribute all its CPUs to its
+ child partitions. There must be at least one cpu left in the
+ parent partition.
+
+ Once becoming a partition root, changes to "cpuset.cpus" is
+ generally allowed as long as the first condition above is true,
+ the change will not take away all the CPUs from the parent
+ partition and the new "cpuset.cpus" value is a superset of its
+ children's "cpuset.cpus" values.
+
+ Sometimes, external factors like changes to ancestors'
+ "cpuset.cpus" or cpu hotplug can cause the state of the partition
+ root to change. On read, the "cpuset.sched.partition" file
+ can show the following values.
+
+ "member" Non-root member of a partition
+ "root" Partition root
+ "root invalid" Invalid partition root
+
+ It is a partition root if the first 2 partition root conditions
+ above are true and at least one CPU from "cpuset.cpus" is
+ granted by the parent cgroup.
+
+ A partition root can become invalid if none of CPUs requested
+ in "cpuset.cpus" can be granted by the parent cgroup or the
+ parent cgroup is no longer a partition root itself. In this
+ case, it is not a real partition even though the restriction
+ of the first partition root condition above will still apply.
+ The cpu affinity of all the tasks in the cgroup will then be
+ associated with CPUs in the nearest ancestor partition.
+
+ An invalid partition root can be transitioned back to a
+ real partition root if at least one of the requested CPUs
+ can now be granted by its parent. In this case, the cpu
+ affinity of all the tasks in the formerly invalid partition
+ will be associated to the CPUs of the newly formed partition.
+ Changing the partition state of an invalid partition root to
+ "member" is always allowed even if child cpusets are present.
+
Device controller
-----------------
--
1.8.3.1
next prev parent reply other threads:[~2018-11-08 15:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-08 15:08 [PATCH v15 00/12] Enable cpuset controller in default hierarchy Waiman Long
2018-11-08 15:08 ` [PATCH v15 01/12] cpuset: " Waiman Long
2018-11-08 15:08 ` [PATCH v15 02/12] cpuset: Define data structures to support scheduling partition Waiman Long
2018-11-08 15:08 ` [PATCH v15 03/12] cpuset: Simply allocation and freeing of cpumasks Waiman Long
2018-11-08 15:08 ` [PATCH v15 04/12] cpuset: Add new v2 cpuset.sched.partition flag Waiman Long
2018-11-08 15:08 ` [PATCH v15 05/12] cpuset: Add an error state to cpuset.sched.partition Waiman Long
2018-11-08 15:08 ` [PATCH v15 06/12] cpuset: Track cpusets that use parent's effective_cpus Waiman Long
2018-11-08 15:08 ` [PATCH v15 07/12] cpuset: Make CPU hotplug work with partition Waiman Long
2018-11-08 15:08 ` [PATCH v15 08/12] cpuset: Make generate_sched_domains() " Waiman Long
2018-11-08 15:08 ` [PATCH v15 09/12] cpuset: Expose cpus.effective and mems.effective on cgroup v2 root Waiman Long
2018-11-08 15:08 ` [PATCH v15 10/12] cpuset: Use descriptive text when reading/writing cpuset.sched.partition Waiman Long
2018-11-08 15:08 ` Waiman Long [this message]
2018-11-08 15:08 ` [PATCH v15 12/12] cpuset: Expose cpuset.cpus.subpartitions with cgroup_debug Waiman Long
2018-11-08 15:46 ` Peter Zijlstra
2018-11-08 18:59 ` Waiman Long
2018-11-08 15:46 ` [PATCH v15 00/12] Enable cpuset controller in default hierarchy Peter Zijlstra
2018-11-08 20:28 ` Tejun Heo
2018-11-08 20:31 ` Waiman Long
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