This patch updates the cgroup-v2.rst file to include information about the new "isolcpus" partition type.

Signed-off-by: Waiman Long longman@redhat.com --- Documentation/admin-guide/cgroup-v2.rst | 89 +++++++++++++++++++------ 1 file changed, 70 insertions(+), 19 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst index f67c0829350b..352a02849fa7 100644 --- a/Documentation/admin-guide/cgroup-v2.rst +++ b/Documentation/admin-guide/cgroup-v2.rst @@ -2225,7 +2225,8 @@ Cpuset Interface Files ========== ===================================== "member" Non-root member of a partition "root" Partition root - "isolated" Partition root without load balancing + "isolcpus" Partition root for isolated CPUs pool + "isolated" Partition root for isolated CPUs ========== =====================================

The root cgroup is always a partition root and its state @@ -2237,24 +2238,41 @@ Cpuset Interface Files its descendants except those that are separate partition roots themselves and their descendants.

+ When set to "isolcpus", the CPUs in that partition root will + be in an isolated state without any load balancing from the + scheduler. This partition root is special as there can be at + most one instance of it in a system and no task or child cpuset + is allowed in this cgroup. It acts as a pool of isolated CPUs to + be pulled into other "isolated" partitions. The "cpuset.cpus" + of an "isolcpus" partition root contains the list of isolated + CPUs it holds, where "cpuset.cpus.effective" contains the list + of freely available isolated CPUs that are ready to be pull + into other "isolated" partition. + When set to "isolated", the CPUs in that partition root 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". - - A partition root ("root" or "isolated") can be in one of the - two possible states - valid or invalid. An invalid partition - root is in a degraded state where some state information may - be retained, but behaves more like a "member". - - All possible state transitions among "member", "root" and - "isolated" are allowed. + individual CPUs for optimal performance. The isolated CPUs can + come from either the parent partition root or from an "isolcpus" + partition if the parent cannot satisfy its request. + + 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 partition subtracts available + CPUs from its parent "cpuset.cpus.effective". An exception is + an "isolated" partition that pulls its isolated CPUs from the + "isolcpus" partition root that is not its direct parent. + + A partition root can be in one of the two possible states - + valid or invalid. An invalid partition root is in a degraded + state where some state information may be retained, but behaves + more like a "member". + + All possible state transitions among "member", "root", "isolcpus" + and "isolated" are allowed. However, the partition root may + not be valid if the corresponding prerequisite conditions are + not met.

On read, the "cpuset.cpus.partition" file can show the following values. @@ -2262,16 +2280,18 @@ Cpuset Interface Files ============================= ===================================== "member" Non-root member of a partition "root" Partition root - "isolated" Partition root without load balancing + "isolcpus" Partition root for isolated CPUs pool + "isolated" Partition root for isolated CPUs "root invalid (<reason>)" Invalid partition root + "isolcpus invalid (<reason>)" Invalid isolcpus partition root "isolated invalid (<reason>)" Invalid isolated partition root ============================= =====================================

In the case of an invalid partition root, a descriptive string on - why the partition is invalid is included within parentheses. + why the partition is invalid may be included within parentheses.

- For a partition root to become valid, the following conditions - must be met. + For a "root" partition root to become 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 +2301,37 @@ Cpuset Interface Files 4) The "cpuset.cpus.effective" cannot be empty unless there is no task associated with this partition.

+ A valid "isolcpus" partition root requires the following + conditions. + + 1) The parent cgroup is a valid partition root. + 2) The "cpuset.cpus" must be a subset of parent's "cpuset.cpus" + including an empty cpu list. + 3) There can be no more than one valid "isolcpus" partition. + 4) No task or child cpuset is allowed. + + Note that an "isolcpus" partition is not exclusive and its + isolated CPUs can be distributed down sibling cgroups even + though they may not appear in their "cpuset.cpus.effective". + + A valid "isolated" partition root can pull isolated CPUs from + either its parent partition or from the "isolcpus" partition. + It also requires the following conditions to be met. + + 1) The "cpuset.cpus" is exclusive with its siblings , i.e. they + are not shared by any of its siblings (exclusivity rule). + 2) The "cpuset.cpus" is not empty and must be a subset of + parent's "cpuset.cpus". + 3) The "cpuset.cpus.effective" cannot be empty unless there is + no task associated with this partition. + + If pulling isolated CPUS from "isolcpus" partition, + the "cpuset.cpus" must also be a subset of "isolcpus" + partition's "cpuset.cpus" and all the requested CPUs must + be available for pulling, i.e. in "isolcpus" partition's + "cpuset.cpus.effective". In this case, its hierarchical parent + does not need to be a valid partition root. + 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