On 5/31/23 09:34, Waiman Long wrote:
This patch updates the cgroup-v2.rst file to include information about
the new "cpuset.cpus.reserve" control file as well as the new remote
partition.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
Documentation/admin-guide/cgroup-v2.rst | 92 +++++++++++++++++++++----
1 file changed, 79 insertions(+), 13 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index f67c0829350b..3e9351c2cd27 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -2215,6 +2215,38 @@ Cpuset Interface Files
Its value will be affected by memory nodes hotplug events.
+ cpuset.cpus.reserve
+ A read-write multiple values file which exists only on root
+ cgroup.
+
+ It lists all the CPUs that are reserved for adjacent and remote
+ partitions created in the system. See the next section for
+ more information on what an adjacent or remote partitions is.
+
+ Creation of adjacent partition does not require touching this
+ control file as CPU reservation will be done automatically.
+ In order to create a remote partition, the CPUs needed by the
+ remote partition has to be written to this file first.
+
+ Due to the fact that "cpuset.cpus.reserve" holds reserve CPUs
+ that can be used by multiple partitions and automatic reservation
+ may also race with manual reservation, an extension prefixes of
+ "+" and "-" are allowed for this file to reduce race.
+
+ A "+" prefix can be used to indicate a list of additional
+ CPUs that are to be added without disturbing the CPUs that are
+ originally there. For example, if its current value is "3-4",
+ echoing ""+5" to it will change it to "3-5".
"+5"
+
+ Once a remote partition is destroyed, its CPUs have to be
+ removed from this file or no other process can use them. A "-"
+ prefix can be used to remove a list of CPUs from it. However,
+ removing CPUs that are currently used in existing partitions
+ may cause those partitions to become invalid. A single "-"
+ character without any number can be used to indicate removal
+ of all the free CPUs not yet allocated to any partitions to
+ avoid accidental partition invalidation.
+
cpuset.cpus.partition
A read-write single value file which exists on non-root
cpuset-enabled cgroups. This flag is owned by the parent cgroup
@@ -2228,25 +2260,49 @@ Cpuset Interface Files
"isolated" Partition root without load balancing
========== =====================================
- The root cgroup is always a partition root and its state
- cannot be changed. All other non-root cgroups start out as
- "member".
+ A cpuset partition is a collection of cgroups with a partition
+ root at the top of the hierarchy and its descendants except
+ those that are separate partition roots themselves and their
+ descendants. A partition has exclusive access to the set of
+ CPUs allocated to it. Other cgroups outside of that partition
+ cannot use any CPUs in that set.
+
+ There are two types of partitions - adjacent and remote. The
+ parent of an adjacent partition must be a valid partition root.
+ Partition roots of adjacent partitions are all clustered around
+ the root cgroup. Creation of adjacent partition is done by
+ writing the desired partition type into "cpuset.cpus.partition".
+
+ A remote partition does not require a partition root parent.
+ So a remote partition can be formed far from the root cgroup.
+ However, its creation is a 2-step process. The CPUs needed
+ by a remote partition ("cpuset.cpus" of the partition root)
+ has to be written into "cpuset.cpus.reserve" of the root
+ cgroup first. After that, "isolated" can be written into
+ "cpuset.cpus.partition" of the partition root to form a remote
+ isolated partition which is the only supported remote partition
+ type for now.
+
+ All remote partitions are terminal as adjacent partition cannot
+ be created underneath it. With the way remote partition is
+ formed, it is not possible to create another valid remote
+ partition underneath it.
+
+ The root cgroup is always a partition root and its state cannot
+ be changed. All other non-root cgroups start out as "member".
When set to "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.
+ partition or scheduling domain.
- When set to "isolated", the CPUs in that partition root will
+ When set to "isolated", the CPUs in that partition will
be in an isolated state without any load balancing from the
scheduler. Tasks placed in such a partition with multiple
CPUs should be carefully distributed and bound to each of the
individual CPUs for optimal performance.
- The value shown in "cpuset.cpus.effective" of a partition root
- is the CPUs that the partition root can dedicate to a potential
- new child partition root. The new child subtracts available
- CPUs from its parent "cpuset.cpus.effective".
+ The value shown in "cpuset.cpus.effective" of a partition root is
+ the CPUs that are dedicated to that partition and not available
+ to cgroups outside of that partittion.
partition.
A partition root ("root" or "isolated") can be in one of the
two possible states - valid or invalid. An invalid partition
@@ -2270,8 +2326,8 @@ Cpuset Interface Files
In the case of an invalid partition root, a descriptive string on
why the partition is invalid is included within parentheses.
- For a partition root to become valid, the following conditions
- must be met.
+ For an adjacent partition root to be valid, the following
+ conditions must be met.
1) The "cpuset.cpus" is exclusive with its siblings , i.e. they
are not shared by any of its siblings (exclusivity rule).
@@ -2281,6 +2337,16 @@ Cpuset Interface Files
4) The "cpuset.cpus.effective" cannot be empty unless there is
no task associated with this partition.
+ For a remote partition root to be valid, the following conditions
+ must be met.
+
+ 1) The same exclusivity rule as adjacent partition root.
+ 2) The "cpuset.cpus" is not empty and all the CPUs must be
+ present in "cpuset.cpus.reserve" of the root cgroup and none
+ of them are allocated to another partition.
+ 3) The "cpuset.cpus" value must be present in all its ancestors
+ to ensure proper hierarchical cpu distribution.
CPU
+
External events like hotplug or changes to "cpuset.cpus" can
cause a valid partition root to become invalid and vice versa.
Note that a task cannot be moved to a cgroup with empty
