This command is used to create, modify, and destroy cpusets. Cpusets form a tree-like structure rooted at
the root cpuset which always includes all system CPUs and all system memory nodes.
A cpuset is an organizational unit that defines a group of CPUs and a group of memory nodes where a
process or thread (i.e. task) is allowed to run on. For non-NUMA machines, the memory node is always 0
(zero) and cannot be set to anything else. For NUMA machines, the memory node can be set to a similar
specification as the CPU definition and will tie those memory nodes to that cpuset. You will usually want
the memory nodes that belong to the CPUs defined to be in the same cpuset.
A cpuset can have exclusive right to the CPUs defined in it. This means that only this cpuset can own
these CPUs. Similarly, a cpuset can have exclusive right to the memory nodes defined in it. This means
that only this cpuset can own these memory nodes.
Cpusets can be specified by name or by path; however, care should be taken when specifying by name if the
name is not unique. This tool will generally not let you do destructive things to non-unique cpuset
names.
Cpusets are uniquely specified by path. The path starts at where the cpusets filesystem is mounted so you
generally do not have to know where that is. For example, so specify a cpuset that is called "two" which
is a subset of "one" which in turn is a subset of the root cpuset, use the path "/one/two" regardless of
where the cpusets filesystem is mounted.
When specifying CPUs, a so-called CPUSPEC is used. The CPUSPEC will accept a comma-separated list of CPUs
and inclusive range specifications. For example, --cpu=1,3,5-7 will assign CPU1, CPU3, CPU5, CPU6, and
CPU7 to the specified cpuset.
Note that cpusets follow certain rules. For example, children can only include CPUs that the parents
already have. If you do not follow those rules, the kernel cpuset subsystem will not let you create that
cpuset. For example, if you create a cpuset that contains CPU3, and then attempt to create a child of
that cpuset with a CPU other than 3, you will get an error, and the cpuset will not be active. The error
is somewhat cryptic in that it is usually a "Permission denied" error.
Memory nodes are specified with a MEMSPEC in a similar way to the CPUSPEC. For example, --mem=1,3-6 will
assign MEM1, MEM3, MEM4, MEM5, and MEM6 to the specified cpuset.
Note that if you attempt to create or modify a cpuset with a memory node specification that is not valid,
you may get a cryptic error message, "No space left on device", and the modification will not be allowed.
When you destroy a cpuset, then the tasks running in that set are moved to the parent of that cpuset. If
this is not what you want, then manually move those tasks to the cpuset of your choice with the csetproc
command (see csetproc--help for more information).
EXAMPLES
Create a cpuset with the default memory specification
#csetset--cpu=2,4,6-8--set=new_set
This command creates a cpuset called "new_set" located off the root cpuset which holds CPUS 2,4,6,7,8 and
node 0 (interleaved) memory. Note that --set is optional, and you can just specify the name for the new
cpuset after all arguments.
Create a cpuset that specifies both CPUs and memory nodes
#csetset--cpu=3--mem=3/rad/set_one
Note that this command uses the full path method to specify the name of the new cpuset "/rad/set_one". It
also names the new cpuset implicitly (i.e. no --set option, although you can use that if you want to). If
the "set_one" name is unique, you can subsequently refer to is just by that. Memory node 3 is assigned to
this cpuset as well as CPU 3.
The above commands will create the new cpusets, or if they already exist, they will modify them to the
new specifications.