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Sets are referenced by a number of type cpuset_id_t. Each thread has a root set, an assigned set, and an anonymous mask. Only the root and assigned sets are numbered. The root set is the set of all CPUs available in the system or in the system partition the thread is running in. The assigned set is a subset of the root set and is administratively assignable on a per-process basis. Many processes and threads may be members of a numbered set.
The anonymous set is a further thread-specific refinement on the assigned set. It is intended that administrators will manipulate numbered sets using cpuset(1) while application developers will manipulate anonymous sets using cpuset_setaffinity(2).
To select the correct set a value of type cpulevel_t is used. The following values for level are supported:
|CPU_LEVEL_WHICH||Set specified by which argument|
The which argument determines how the value of id is interpreted and is of type cpuwhich_t. The which argument may have the following values:
|CPU_WHICH_TID||id is lwpid_t (thread id)|
|CPU_WHICH_PID||id is pid_t (process id)|
|CPU_WHICH_JAIL||id is jid (jail id)|
|CPU_WHICH_CPUSET||id is a cpusetid_t (cpuset id)|
|CPU_WHICH_IRQ||id is an irq number|
|CPU_WHICH_DOMAIN||id is a NUMA domain|
An id of '-1' may be used with a which of CPU_WHICH_TID, CPU_WHICH_PID, or CPU_WHICH_CPUSET to mean the current thread, process, or current thread's cpuset. All cpuset syscalls allow this usage.
A level argument of CPU_LEVEL_WHICH combined with a which argument other than CPU_WHICH_CPUSET refers to the anonymous mask of the object. This mask does not have an id and may only be manipulated with cpuset_setaffinity(2).
cpuset() creates a new set containing the same CPUs as the root set of the current process and stores its id in the space provided by setid. On successful completion the calling process joins the set and is the only member. Children inherit this set after a call to fork(2).
cpuset_setid() attempts to set the id of the object specified by the which argument. Currently CPU_WHICH_PID is the only acceptable value for which as threads do not have an id distinct from their process and the API does not permit changing the id of an existing set. Upon successful completion all of the threads in the target process will be running on CPUs permitted by the set.
cpuset_getid() retrieves a set id from the object indicated by which and stores it in the space pointed to by setid. The retrieved id may be that of either the root or assigned set depending on the value of level. level should be CPU_LEVEL_CPUSET or CPU_LEVEL_ROOT to get the set id from the process or thread specified by the id argument. Specifying CPU_LEVEL_WHICH with a process or thread is unsupported since this references the unnumbered anonymous mask.
|The which or level argument was not a valid value.|
|The cpuset_setid() call would leave a thread without a valid CPU to run on because the set does not overlap with the thread's anonymous mask.|
|The setid pointer passed to cpuset_getid() or cpuset() was invalid.|
|The object specified by the id and which arguments could not be found.|
|The calling process did not have the credentials required to complete the operation.|
|There was no free cpusetid_t for allocation.|
|CPUSET (2)||October 20, 2015|
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|“||I think Unix and snowflakes are the only two classes of objects in the universe in which no two instances ever match exactly.||”|
|— Noel Chiappa|