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CPUSET(2)		       System Calls Manual		       CPUSET(2)

NAME
     cpuset, cpuset_getid, cpuset_setid -- manage CPU affinity sets

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/param.h>
     #include <sys/cpuset.h>

     int
     cpuset(cpusetid_t *setid);

     int
     cpuset_setid(cpuwhich_t which, id_t id, cpusetid_t setid);

     int
     cpuset_getid(cpulevel_t level, cpuwhich_t which, id_t id,
	 cpusetid_t *setid);

DESCRIPTION
     The  cpuset  family  of  system calls allow applications to control sets of
     processors and assign processes and threads to these sets.  Processor  sets
     contain  lists  of  CPUs  that members may run on and exist only as long as
     some process is a member of the set.  All processes in the system	have  an
     assigned  set.   The default set for all processes in the system is the set
     numbered 1.  Threads belong to the same set as the process  which	contains
     them,  however, they may further restrict their set with the anonymous per-
     thread mask.

     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 as-
     signed 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  as-
     signed  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  us-
     ing  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  follow-
     ing values for level are supported:

	   CPU_LEVEL_ROOT      Root set
	   CPU_LEVEL_CPUSET    Assigned set
	   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 lpwid_t (thread id)
	   CPU_WHICH_PID       id is pid_t (process id)
	   CPU_WHICH_CPUSET    id is a cpusetid_t (cpuset id)
	   CPU_WHICH_IRQ       id is an irq number

     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_setaffin-
     ity(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  suc-
     cessful  completion  the calling process joins the set and is the only mem-
     ber.  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 unnum-
     bered anonymous mask.

     The actual contents of the sets  may  be  retrieved  or  manipulated  using
     cpuset_getaffinity(2)  and  cpuset_setaffinity(2).   See those manual pages
     for more detail.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the value -1
     is returned and the global variable errno is set to indicate the error.

ERRORS
     The following error codes may be set in errno:

     [EINVAL]		The which or level argument was not a valid value.

     [EDEADLK]		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.

     [EFAULT]		The setid pointer passed to cpuset_getid()  or	cpuset()
			was invalid.

     [ESRCH]		The object specified by the id and which arguments could
			not be found.

     [EPERM]		The  calling  process  did  not have the credentials re-
			quired to complete the operation.

     [ENFILE]		There was no free cpusetid_t() for allocation.

SEE ALSO
     cpuset(1), cpuset_getaffinity(2), cpuset_setaffinity(2), CPU_SET(3)

HISTORY
     The cpuset family of system calls first appeared in FreeBSD 7.1.

AUTHOR
     Jeffrey Roberson <jeff@FreeBSD.org>

FreeBSD 7.1			 March 29, 2008 		       CPUSET(2)
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