xref: /netbsd-src/lib/libpthread/affinity.3 (revision 6533efb1502b0c4634f371815c31eecef5b09dc1)

.\"	$NetBSD: affinity.3,v 1.8 2011/12/05 10:27:40 wiz Exp $
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.\" by Mindaugas Rasiukevicius <rmind at NetBSD org>.
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.Dd December 4, 2011
.Dt AFFINITY 3
.Os
.Sh NAME
.Nm pthread_setaffinity_np ,
.Nm pthread_getaffinity_np
.Nd affinity of threads
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.In sched.h
.Ft int
.Fn pthread_setaffinity_np "pthread_t thread" "size_t size" "cpuset_t *set"
.Ft int
.Fn pthread_getaffinity_np "pthread_t thread" "size_t size" "cpuset_t *set"
.Sh DESCRIPTION
Thread affinity allows to run the thread on specified CPU or CPUs only.
.Pp
The
.Fn pthread_setaffinity_np
function sets the affinity mask
.Fa set
for
.Fa thread .
At least one valid CPU must be set in the mask.
.Pp
The
.Fn pthread_getaffinity_np
function gets the affinity mask of
.Fa thread
into
.Fa set .
Note that
.Fa set
must be created and initialized using the
.Xr cpuset 3
functions.
.Sh IMPLEMENTATION NOTES
Setting CPU
.Nm
requires super-user privileges.
Ordinary users can be allowed to control CPU affinity
of their threads via the
.Pa security.models.extensions.user_set_cpu_affinity
.Xr sysctl 7 .
See
.Xr secmodel_extensions 9 .
.Pp
Portable applications should not use the
.Fn pthread_setaffinity_np
and
.Fn pthread_getaffinity_np
functions.
.Sh RETURN VALUES
The
.Fn pthread_setaffinity_np
and
.Fn pthread_getaffinity_np
functions return 0 on success.
Otherwise, an error number is returned to indicate the error.
.Sh EXAMPLES
An example of code fragment, which sets the affinity for the current
thread to the CPU whose ID is 0:
.Bd -literal
	cpuset_t *cset;
	pthread_t pth;
	cpuid_t ci;

	cset = cpuset_create();
	if (cset == NULL) {
		err(EXIT_FAILURE, "cpuset_create");
	}
	ci = 0;
	cpuset_set(ci, cset);

	pth = pthread_self();
	error = pthread_setaffinity_np(pth, cpuset_size(cset), cset);
	if (error) {
		...
	}
	cpuset_destroy(cset);
.Ed
.Sh COMPATIBILITY
Both functions are non-standard extensions.
.Sh ERRORS
Both functions may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The specified
.Fa set
was invalid.
.It Bq Er EPERM
The calling process lacks the appropriate privileges to perform
the operation.
.It Bq Er ESRCH
No thread could be found corresponding to the one specified by
.Fa thread .
.El
.Sh NOTES
There is an alternative processor sets interface, see
.Xr pset 3 .
However, thread affinity and processor sets are mutually exclusive,
hence mixing of these interfaces is prohibited.
.Sh SEE ALSO
.Xr cpuset 3 ,
.Xr pset 3 ,
.Xr pthread_getschedparam 3 ,
.Xr pthread_setschedparam 3 ,
.Xr sched 3 ,
.Xr schedctl 8