Hi,
Just a few small nits below:
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
--
~Randy
