lgrp_affinity_get(3LGRP)				 Locality Group Library Functions				  lgrp_affinity_get(3LGRP)

NAME

       lgrp_affinity_get, lgrp_affinity_set - get of set lgroup affinity

SYNOPSIS

       cc [ flag ... ] file... -llgrp [ library ... ]
       #include <sys/lgrp_user.h>

       lgrp_affinity_t lgrp_affinity_get(idtype_t idtype, id_t id, lgrp_id_t lgrp);

       int lgrp_affinity_set(idtype_t idtype, id_t id, lgrp_id_t lgrp, lgrp_affinity_t affinity);

DESCRIPTION

       The  lgrp_affinity_get()  function  returns  the affinity that the LWP or set of LWPs specified by the idtype and id arguments have for the
       given lgroup.

       The lgrp_affinity_set() function sets the affinity that the LWP or set of LWPs specified by idtype and id have for the given  lgroup.   The
       lgroup affinity can be set to LGRP_AFF_STRONG, LGRP_AFF_WEAK, or LGRP_AFF_NONE.

       If the idtype is P_PID, the affinity is retrieved for one of the LWPs in the process or set for all the LWPs of the process with process ID
       (PID) id. The affinity is retrieved or set for the LWP of the current process with LWP ID id if idtype is P_LWPID.  If id is  P_MYID,  then
       the current LWP or process is specified.

       The  operating system uses the lgroup affinities as advice on where to run a thread and allocate its memory and factors this advice in with
       other constraints.  Processor binding and processor sets can restrict which lgroups a thread can run on,  but  do  not  change  the  lgroup
       affinities.

       Each thread can have an affinity for an lgroup in the system such that the thread will tend to be scheduled to run on that lgroup and allo-
       cate memory from there whenever possible.  If the thread has affinity for more than one lgroup, the operating system will try  to  run  the
       thread  and  allocate  its memory on the lgroup for which it has the strongest affinity, then the next strongest, and so on up through some
       small, system-dependent number of these lgroup affinities.  When multiple lgroups have the same affinity, the  order  of  preference  among
       them  is  unspecified and up to the operating system to choose.	The lgroup with the strongest affinity that the thread can run on is known
       as its "home lgroup" (see lgrp_home(3LGRP)) and is usually the operating system's first choice of where to run the thread and allocate  its
       memory.

	There are different levels of affinity that can be specified by a thread for a particuliar lgroup.  The levels of affinity are the follow-
       ing from strongest to weakest:

       LGRP_AFF_STRONG	       /* strong affinity */
       LGRP_AFF_WEAK	       /* weak affinity */
       LGRP_AFF_NONE	       /* no affinity */

       The LGRP_AFF_STRONG affinity serves as a hint to the operating system that the calling thread has a strong affinity for the  given  lgroup.
       If this is the thread's home lgroup, the operating system will avoid rehoming it to another lgroup if possible.	However, dynamic reconfig-
       uration, processor offlining, processor binding, and processor set binding and manipulation are examples of events that can cause the oper-
       ating system to change the thread's home lgroup for which it has a strong affinity.

       The LGRP_AFF_WEAK affinity is a hint to the operating system that the calling thread has a weak affinity for the given lgroup.  If a thread
       has a weak affinity for its home lgroup, the operating system interpets this to mean that thread does  not  mind  whether  it  is  rehomed,
       unlike LGRP_AFF_STRONG.	Load balancing, dynamic reconfiguration, processor binding, or processor set binding and manipulation are examples
       of events that can cause the operating system to change a thread's home lgroup for which it has a weak affinity.

       The LGRP_AFF_NONE affinity signifies no affinity and can be used to remove a thread's affinity for a particuliar lgroup.   Initially,  each
       thread  has no affinity to any lgroup.  If a thread has no lgroup affinities set, the operating system chooses a home lgroup for the thread
       with no affinity set.

RETURN VALUES

       Upon successful completion, lgrp_affinity_get() returns the affinity for the given lgroup.

       Upon successful completion, lgrp_affinity_set() return 0.

       Otherwise, both functions return -1 and set errno to indicate the error.

ERRORS

       The lgrp_affinity_get() and lgrp_affinity_set() functions will fail if:

       EINVAL	       The specified lgroup, affinity, or ID type is not valid.

       EPERM	       The effective user of the calling process does not have appropriate privileges, and its real or effective user ID does  not
		       match the real or effective user ID of one of the LWPs.

       ESRCH	       The specified lgroup or LWP(s) was not found.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       lgrp_home(3LGRP), liblgrp(3LIB), attributes(5)

SunOS 5.10							    16 Apr 2003 					  lgrp_affinity_get(3LGRP)