man3/pthread_setaffinity_np.3

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  26 .TH PTHREAD_SETAFFINITY_NP 3 2016-03-15 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 pthread_setaffinity_np, pthread_getaffinity_np \- set/get
  29 CPU affinity of a thread
  30 .SH SYNOPSIS
  31 .nf
  32 .BR "#define _GNU_SOURCE" "             /* See feature_test_macros(7) */"
  33 .B #include <pthread.h>
  34
  35 .BI "int pthread_setaffinity_np(pthread_t " thread ", size_t " cpusetsize ,
  36 .BI "                           const cpu_set_t *" cpuset );
  37 .BI "int pthread_getaffinity_np(pthread_t " thread ", size_t " cpusetsize ,
  38 .BI "                           cpu_set_t *" cpuset );
  39 .sp
  40 Compile and link with \fI\-pthread\fP.
  41 .fi
  42 .SH DESCRIPTION
  43 The
  44 .BR pthread_setaffinity_np ()
  45 function
  46 sets the CPU affinity mask of the thread
  47 .I thread
  48 to the CPU set pointed to by
  49 .IR cpuset .
  50 If the call is successful,
  51 and the thread is not currently running on one of the CPUs in
  52 .IR cpuset ,
  53 then it is migrated to one of those CPUs.
  54
  55 The
  56 .BR pthread_getaffinity_np ()
  57 function returns the CPU affinity mask of the thread
  58 .I thread
  59 in the buffer pointed to by
  60 .IR cpuset .
  61
  62 For more details on CPU affinity masks, see
  63 .BR sched_setaffinity (2).
  64 For a description of a set of macros
  65 that can be used to manipulate and inspect CPU sets, see
  66 .BR CPU_SET (3).
  67
  68 The argument
  69 .I cpusetsize
  70 is the length (in bytes) of the buffer pointed to by
  71 .IR cpuset .
  72 Typically, this argument would be specified as
  73 .IR sizeof(cpu_set_t) .
  74 (It may be some other value, if using the macros described in
  75 .BR CPU_SET (3)
  76 for dynamically allocating a CPU set.)
  77 .SH RETURN VALUE
  78 On success, these functions return 0;
  79 on error, they return a nonzero error number.
  80 .SH ERRORS
  81 .TP
  82 .B EFAULT
  83 A supplied memory address was invalid.
  84 .TP
  85 .B EINVAL
  86 .RB ( pthread_setaffinity_np ())
  87 The affinity bit mask
  88 .I mask
  89 contains no processors that are currently physically on the system
  90 and permitted to the thread according to any restrictions that
  91 may be imposed by the "cpuset" mechanism described in
  92 .BR cpuset (7).
  93 .TP
  94 .BR EINVAL
  95 .RB ( pthread_setaffinity_np ())
  96 .I cpuset
  97 specified a CPU that was outside the set supported by the kernel.
  98 (The kernel configuration option
  99 .BR CONFIG_NR_CPUS
 100 defines the range of the set supported by the kernel data type
 101 .\" cpumask_t
 102 used to represent CPU sets.)
 103 .\" The raw sched_getaffinity() system call returns the size (in bytes)
 104 .\" of the cpumask_t type.
 105 .TP
 106 .B EINVAL
 107 .RB ( pthread_getaffinity_np ())
 108 .I cpusetsize
 109 is smaller than the size of the affinity mask used by the kernel.
 110 .TP
 111 .B ESRCH
 112 No thread with the ID
 113 .I thread
 114 could be found.
 115 .SH VERSIONS
 116 These functions are provided by glibc since version 2.3.4.
 117 .SH ATTRIBUTES
 118 For an explanation of the terms used in this section, see
 119 .BR attributes (7).
 120 .TS
 121 allbox;
 122 lbw25 lb lb
 123 l l l.
 124 Interface       Attribute       Value
 125 T{
 126 .BR pthread_setaffinity_np (),
 127 .BR pthread_getaffinity_np ()
 128 T}      Thread safety   MT-Safe
 129 .TE
 130 .SH CONFORMING TO
 131 These functions are nonstandard GNU extensions;
 132 hence the suffix "_np" (nonportable) in the names.
 133 .SH NOTES
 134 After a call to
 135 .BR pthread_setaffinity_np (),
 136 the set of CPUs on which the thread will actually run is
 137 the intersection of the set specified in the
 138 .I cpuset
 139 argument and the set of CPUs actually present on the system.
 140 The system may further restrict the set of CPUs on which the thread
 141 runs if the "cpuset" mechanism described in
 142 .BR cpuset (7)
 143 is being used.
 144 These restrictions on the actual set of CPUs on which the thread
 145 will run are silently imposed by the kernel.
 146
 147 These functions are implemented on top of the
 148 .BR sched_setaffinity (2)
 149 and
 150 .BR sched_getaffinity (2)
 151 system calls.
 152
 153 In glibc 2.3.3 only,
 154 versions of these functions were provided that did not have a
 155 .I cpusetsize
 156 argument.
 157 Instead the CPU set size given to the underlying system calls was always
 158 .IR sizeof(cpu_set_t) .
 159
 160 A new thread created by
 161 .BR pthread_create (3)
 162 inherits a copy of its creator's CPU affinity mask.
 163 .SH EXAMPLE
 164 In the following program, the main thread uses
 165 .BR pthread_setaffinity_np ()
 166 to set its CPU affinity mask to include CPUs 0 to 7
 167 (which may not all be available on the system),
 168 and then calls
 169 .BR pthread_getaffinity_np ()
 170 to check the resulting CPU affinity mask of the thread.
 171
 172 .nf
 173 #define _GNU_SOURCE
 174 #include <pthread.h>
 175 #include <stdio.h>
 176 #include <stdlib.h>
 177 #include <errno.h>
 178
 179 #define handle_error_en(en, msg) \\
 180         do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
 181
 182 int
 183 main(int argc, char *argv[])
 184 {
 185     int s, j;
 186     cpu_set_t cpuset;
 187     pthread_t thread;
 188
 189     thread = pthread_self();
 190
 191     /* Set affinity mask to include CPUs 0 to 7 */
 192
 193     CPU_ZERO(&cpuset);
 194     for (j = 0; j < 8; j++)
 195         CPU_SET(j, &cpuset);
 196
 197     s = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
 198     if (s != 0)
 199         handle_error_en(s, "pthread_setaffinity_np");
 200
 201     /* Check the actual affinity mask assigned to the thread */
 202
 203     s = pthread_getaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
 204     if (s != 0)
 205         handle_error_en(s, "pthread_getaffinity_np");
 206
 207     printf("Set returned by pthread_getaffinity_np() contained:\\n");
 208     for (j = 0; j < CPU_SETSIZE; j++)
 209         if (CPU_ISSET(j, &cpuset))
 210             printf("    CPU %d\\n", j);
 211
 212     exit(EXIT_SUCCESS);
 213 }
 214 .fi
 215 .SH SEE ALSO
 216 .BR sched_setaffinity (2),
 217 .BR CPU_SET (3),
 218 .BR pthread_attr_setaffinity_np (3),
 219 .BR pthread_self (3),
 220 .BR sched_getcpu (3),
 221 .BR cpuset (7),
 222 .BR pthreads (7),
 223 .BR sched (7)