Messages in this thread | | | Date | Thu, 1 Jun 2023 09:30:40 -0400 | Subject | Re: [PATCH v2 5/6] cgroup/cpuset: Documentation update for partition | From | Waiman Long <> |
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On 5/31/23 19:11, Randy Dunlap wrote: > Hi, > > Just a few small nits below:
Thanks for catching that.
Cheers, Longman
> > 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@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". > "+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
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