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   6 .TH LGRP_AFFINITY_GET 3LGRP "Apr 16, 2003"
   7 .SH NAME
   8 lgrp_affinity_get, lgrp_affinity_set \- get of set lgroup affinity
  10 .LP
  11 .nf
  12 cc [ \fIflag \&.\|.\|.\fR ] \fIfile\fR\&.\|.\|. \fB-llgrp\fR [ \fIlibrary \&.\|.\|.\fR ]
  13 #include <sys/lgrp_user.h>
  15 \fBlgrp_affinity_t\fR \fBlgrp_affinity_get\fR(\fBidtype_t\fR \fIidtype\fR, \fBid_t\fR \fIid\fR,
  16      \fBlgrp_id_t\fR \fIlgrp\fR);
  17 .fi
  19 .LP
  20 .nf
  21 \fBint\fR \fBlgrp_affinity_set\fR(\fBidtype_t\fR \fIidtype\fR, \fBid_t\fR \fIid\fR, \fBlgrp_id_t\fR \fIlgrp\fR,
  22      \fBlgrp_affinity_t\fR \fIaffinity\fR);
  23 .fi
  26 .LP
  27 The \fBlgrp_affinity_get()\fR function returns the affinity that the LWP or set
  28 of LWPs specified by the \fIidtype\fR and \fIid\fR arguments have for the given
  29 lgroup.
  30 .sp
  31 .LP
  32 The \fBlgrp_affinity_set()\fR function sets the affinity that the LWP or set of
  33 LWPs specified by \fIidtype\fR and \fIid\fR have for the given lgroup.  The
  34 lgroup affinity can be set to \fBLGRP_AFF_STRONG\fR, \fBLGRP_AFF_WEAK\fR, or
  36 .sp
  37 .LP
  38 If the \fIidtype\fR is \fBP_PID\fR, the affinity is retrieved for one of the
  39 LWPs in the process or set for all the LWPs of the process with process ID
  40 (PID) \fIid\fR. The affinity is retrieved or set for the LWP of the current
  41 process with LWP ID \fIid\fR if \fIidtype\fR is \fBP_LWPID\fR.  If \fIid\fR is
  42 \fBP_MYID\fR, then the current LWP or process is specified.
  43 .sp
  44 .LP
  45 The operating system uses the lgroup affinities as advice on where to run a
  46 thread and allocate its memory and factors this advice in with other
  47 constraints.  Processor binding and processor sets can restrict which lgroups a
  48 thread can run on, but do not change the lgroup affinities.
  49 .sp
  50 .LP
  51 Each thread can have an affinity for an lgroup in the system such that the
  52 thread will tend to be scheduled to run on that lgroup and allocate memory from
  53 there whenever possible.  If the thread has affinity for more than one lgroup,
  54 the operating system will try to run the thread and allocate its memory on the
  55 lgroup for which it has the strongest affinity, then the next strongest, and so
  56 on up through some small, system-dependent number of these lgroup affinities.
  57 When multiple lgroups have the same affinity, the order of preference among
  58 them is unspecified and up to the operating system to choose.  The lgroup with
  59 the strongest affinity that the thread can run on is known as its "home lgroup"
  60 (see \fBlgrp_home\fR(3LGRP)) and is usually the operating system's first choice
  61 of where to run the thread and allocate its memory.
  62 .sp
  63 .LP
  64 There are different levels of affinity that can be specified by a thread for a
  65 particular lgroup.  The levels of affinity are the following from strongest to
  66 weakest:
  67 .sp
  68 .in +2
  69 .nf
  70 LGRP_AFF_STRONG         /* strong affinity */
  71 LGRP_AFF_WEAK           /* weak affinity */
  72 LGRP_AFF_NONE           /* no affinity */
  73 .fi
  74 .in -2
  76 .sp
  77 .LP
  78 The \fBLGRP_AFF_STRONG\fR affinity serves as a hint to the operating system
  79 that the calling thread has a strong affinity for the given lgroup.  If this is
  80 the thread's home lgroup, the operating system will avoid rehoming it to
  81 another lgroup if possible.  However, dynamic reconfiguration, processor
  82 offlining, processor binding, and processor set binding and manipulation are
  83 examples of events that can cause the operating system to change the thread's
  84 home lgroup for which it has a strong affinity.
  85 .sp
  86 .LP
  87 The \fBLGRP_AFF_WEAK\fR affinity is a hint to the operating system that the
  88 calling thread has a weak affinity for the given lgroup.  If a thread has a
  89 weak affinity for its home lgroup, the operating system interpets this to mean
  90 that thread does not mind whether it is rehomed, unlike \fBLGRP_AFF_STRONG\fR.
  91 Load balancing, dynamic reconfiguration, processor binding, or processor set
  92 binding and manipulation are examples of events that can cause the operating
  93 system to change a thread's home lgroup for which it has a weak affinity.
  94 .sp
  95 .LP
  96 The \fBLGRP_AFF_NONE\fR affinity signifies no affinity and can be used to
  97 remove a thread's affinity for a particular lgroup.  Initially, each thread
  98 has no affinity to any lgroup.  If a thread has no lgroup affinities set, the
  99 operating system chooses a home lgroup for the thread with no affinity set.
 101 .LP
 102 Upon successful completion, \fBlgrp_affinity_get()\fR returns the affinity for
 103 the given lgroup.
 104 .sp
 105 .LP
 106 Upon successful completion, \fBlgrp_affinity_set()\fR return 0.
 107 .sp
 108 .LP
 109 Otherwise, both functions return \(mi1 and set \fBerrno\fR to indicate the
 110 error.
 112 .LP
 113 The \fBlgrp_affinity_get()\fR and \fBlgrp_affinity_set()\fR functions will fail
 114 if:
 115 .sp
 116 .ne 2
 117 .na
 118 \fB\fBEINVAL\fR\fR
 119 .ad
 120 .RS 10n
 121 The specified lgroup, affinity, or ID type is not valid.
 122 .RE
 124 .sp
 125 .ne 2
 126 .na
 127 \fB\fBEPERM\fR\fR
 128 .ad
 129 .RS 10n
 130 The effective user of the calling process does not have appropriate privileges,
 131 and its real or effective user ID does not match the real or effective user ID
 132 of one of the LWPs.
 133 .RE
 135 .sp
 136 .ne 2
 137 .na
 138 \fB\fBESRCH\fR\fR
 139 .ad
 140 .RS 10n
 141 The specified lgroup or LWP(s) was not found.
 142 .RE
 145 .LP
 146 See \fBattributes\fR(5) for descriptions of the following attributes:
 147 .sp
 149 .sp
 150 .TS
 151 box;
 152 c | c
 153 l | l .
 155 _
 156 Interface Stability     Evolving
 157 _
 158 MT-Level        MT-Safe
 159 .TE
 162 .LP
 163 \fBlgrp_home\fR(3LGRP), \fBliblgrp\fR(3LIB), \fBattributes\fR(5)