PSET(3) Library Functions Manual PSET(3)

pset_create, pset_assign, pset_bind, pset_destroy — processor sets

POSIX Real-time Library (librt, -lrt)

#include <sys/pset.h>

int
pset_create(psetid_t *psid);

int
pset_assign(psetid_t psid, cpuid_t cpuid, psetid_t *opsid);

int
pset_bind(psetid_t psid, idtype_t type, id_t id, psetid_t *opsid);

int
pset_destroy(psetid_t psid);

The processor sets API provides the possibility to exclusively dedicate specific processors or groups of processors to processes or threads. After processes or threads are bound to a group of processors by the API, the group henceforth runs only those processes or threads. This section describes the functions used to control processor sets.

(psid)
Creates a processor set, and returns its ID into psid.
(psid, cpu, opsid)
Assigns the processor specified by cpuid to the processor set specified by psid. Stores the current processor set ID of the processor or PS_NONE into opsid, if the pointer is not NULL.

The following actions can be specified:

  1. If psid is set to PS_QUERY, then the current processor set ID will be returned into psid, and no assignment will be performed.
  2. If psid is set to PS_MYID, then the processor set ID of the calling process will be used, and psid will be ignored.
  3. If psid is set to PS_NONE, any assignment to the processor will be cleared.
(psid, type, id, opsid)
Dedicates the processor set specified by psid to the target specified by id. The current processor set ID to which the target is bound or PS_NONE will be returned in opsid, if the pointer is not NULL. NetBSD supports the following types of targets specified by type:
Process identified by the PID.
Thread of the calling process identified by the LID.

The following actions can be specified:

  1. If psid is set to PS_QUERY, then the current processor set ID to which the target is bound or PS_NONE will be returned in opsid, and no binding will be performed.
  2. If psid is set to PS_MYID, then the processor set ID of the calling process will be used.
  3. If psid is set to PS_NONE, the specified target will be unbound from the processor set.
(psid)
Destroys the processor set specified by psid. Before destroying the processor set, all related assignments of the processors will be cleared, and all bound threads will be unbound.

If psid is PS_MYID, the processor set ID of the caller thread will be used.

Except for PS_QUERY operations, these interfaces require super-user privileges.

The pset_bind() function can return the current processor set ID to which the target is bound, or PS_NONE. However, for example, the process may have many threads, which could be bound to different processor sets. In such a case it is unspecified which thread will be used to return the information.

There is an alternative thread affinity interface, see affinity(3). However, processor sets and thread affinity are mutually exclusive, hence mixing of these interfaces is prohibited.

Upon successful completion these functions return 0. Otherwise, -1 is returned and errno is set to indicate the error.

An example of code fragment, which assigns the CPU whose ID is 0, for current process:

	psetid_t psid;
	cpuid_t ci = 0;

	if (pset_create(&psid) < 0)
		err(EXIT_FAILURE, "pset_create");

	/* Assign CPU 0 to the processor-set */
	if (pset_assign(psid, ci, NULL) < 0)
		err(EXIT_FAILURE, "pset_assign");

	/* Bind the current process to the processor-set */
	if (pset_bind(psid, P_PID, P_MYID, NULL) < 0)
		err(EXIT_FAILURE, "pset_bind");

	/*
	 * At this point, CPU 0 runs only the current process.
	 */
	perform_work();

	if (pset_destroy(psid) < 0)
		err(EXIT_FAILURE, "pset_destroy");

The pset_create() function fails if:

[]
No memory is available for creation of the processor set, or limit of the allowed count of the processor sets was reached.
[]
The calling process is not the super-user.

The pset_assign() function fails if:

[]
Another operation is performing on the processor set.
[]
psid or cpuid are invalid.
[]
The calling process is not the super-user, and psid is not PS_QUERY.

The pset_bind() function fails if:

[]
Another operation is performing on the processor set.
[]
psid or type are invalid.
[]
The calling process is not the super-user, and psid is not PS_QUERY.
[]
The specified target was not found.

The pset_destroy() function fails if:

[]
Another operation is performing on the processor set.
[]
The calling process is not the super-user.

affinity(3), cpuset(3), sched(3), schedctl(8)

This API is expected to be compatible with the APIs found in Solaris and HP-UX operating systems.

The processor sets appeared in NetBSD 5.0.

February 21, 2025 NetBSD 11.0