Update Documentation/admin-guide/cgroup-v2.rst on the newly introduced "isolated" cpuset partition type as well as the ability to create non-top cpuset partition with no cpu allocated to it.
Signed-off-by: Waiman Long firstname.lastname@example.org --- Documentation/admin-guide/cgroup-v2.rst | 65 +++++++++++++++++-------- 1 file changed, 44 insertions(+), 21 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index b1e81aa8598a..cf40a7f499c0 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2010,8 +2010,9 @@ Cpuset Interface Files It accepts only the following input values when written to.
======== ================================ - "root" a partition root - "member" a non-root member of a partition + "member" Non-root member of a partition + "root" Partition root + "isolated" Partition root without load balancing ======== ================================
When set to be a partition root, the current cgroup is the @@ -2020,6 +2021,11 @@ Cpuset Interface Files partition roots themselves and their descendants. The root cgroup is always a partition root.
+ With "isolated", the CPUs in that partition root will be in an + isolated state without any load balancing from the scheduler. + Tasks in such a partition must be explicitly bind to each + individual CPU. + 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. @@ -2038,12 +2044,25 @@ Cpuset Interface Files 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. + A parent partition may distribute all its CPUs to its child + partitions as long as it is not the root cgroup and there is no + task directly associated with that parent partition. Otherwise, + there must be at least one cpu left in the parent partition. + A new task cannot be moved to a partition root with no effective + cpu.
Once becoming a partition root, changes to "cpuset.cpus" is - generally allowed as long as the first condition above is true, + generally allowed as long as the first condition above is true. + Other constraints for this operation are as follows. + + 1) Any newly added CPUs must be a subset of the parent's + "cpuset.cpus.effective". + 2) Taking away all the CPUs from the parent's "cpuset.cpus.effective" + is only allowed if there is no task associated with the + parent partition. + 3) Deletion of CPUs that have been distributed to child partition + roots are not allowed. + 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. @@ -2056,6 +2075,7 @@ Cpuset Interface Files ============== ============================== "member" Non-root member of a partition "root" Partition root + "isolated" Partition root without load balancing "root invalid" Invalid partition root ============== ==============================
@@ -2063,21 +2083,24 @@ Cpuset Interface Files 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. + A partition root becomes invalid if all the CPUs requested in + "cpuset.cpus" become unavailable. This can happen if all the + CPUs have been offlined, or the state of an ancestor partition + root become invalid. 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. In the special case of a parent partition + competing with a child partition for the only CPU left, the + parent partition wins and the child partition becomes invalid. + + An invalid partition root can be transitioned back to a real + partition root if at least one of the requested CPUs become + available again. 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.