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 longman@redhat.com --- Documentation/admin-guide/cgroup-v2.rst | 94 +++++++++++++++---------- 1 file changed, 58 insertions(+), 36 deletions(-)
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index 5c7377b5bd3e..2e101a353ab1 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2080,8 +2080,9 @@ 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 @@ -2090,9 +2091,14 @@ Cpuset Interface Files 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. + When set to "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 bound + to each individual CPU. + + There are constraints on where a partition root can be set + ("root" or "isolated"). 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. @@ -2103,51 +2109,67 @@ Cpuset Interface Files 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 + Setting it to a 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. + 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 + (cpu exclusivity rule) is true. Other constraints for this + operation are as follows.
- 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. + 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.
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. + root to change. On read, the "cpuset.cpus.partition" file can + show the following values.
============== ============================== "member" Non-root member of a partition "root" Partition root + "isolated" Partition root without load balancing "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. + 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 cpu exclusivity rule 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. However changing a partition root back + to member will not be allowed if child partitions are present. + + Poll and inotify events are triggered when transition to or + from invalid partition root happens.
Device controller