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@redhat.com --- 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". + + 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.
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. + 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