pthread_setaffinity_np man page on Scientific

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       pthread_setaffinity_np,	pthread_getaffinity_np	- set/get CPU affinity
       of a thread

       #define _GNU_SOURCE
       #include <pthread.h>

       int pthread_setaffinity_np(pthread_t thread, size_t cpusetsize,
				  const cpu_set_t *cpuset);
       int pthread_getaffinity_np(pthread_t thread, size_t cpusetsize,
				  cpu_set_t *cpuset);

       Compile and link with -pthread.

       The pthread_setaffinity_np() sets the CPU affinity mask of  the	thread
       thread to the CPU set pointed to by cpuset.  If the call is successful,
       and the thread is not currently running on one of the CPUs  in  cpuset,
       then it is migrated to one of those CPUs.

       The  pthread_getaffinity_np() function returns the CPU affinity mask of
       the thread thread in the buffer pointed to by cpuset.

       For more details on CPU affinity masks, see sched_setaffinity(2).   For
       a  description  of  a  set of macros that can be used to manipulate and
       inspect CPU sets, see CPU_SET(3).

       The argument cpusetsize is the length (in bytes) of the buffer  pointed
       to   by	cpuset.	  Typically,  this  argument  would  be	 specified  as
       sizeof(cpu_set_t).  (It may be some other value, if  using  the	macros
       described in CPU_SET(3) for dynamically allocating a CPU set.)

       On  success, these functions return 0; on error, they return a non-zero
       error number.

       EFAULT A supplied memory address was invalid.

       EINVAL (pthread_setaffinity_np()) The affinity bit mask	mask  contains
	      no  processors  that  are currently physically on the system and
	      permitted to the thread according to any restrictions  that  may
	      be imposed by the "cpuset" mechanism described in cpuset(7).

       EINVAL (pthread_setaffinity_np())  cpuset specified a CPU that was out‐
	      side the set supported by the kernel.  (The kernel configuration
	      option  CONFIG_NR_CPUS defines the range of the set supported by
	      the kernel data type used to represent CPU sets.)

       EINVAL (pthread_getaffinity_np()) cpusetsize is smaller than  the  size
	      of the affinity mask used by the kernel.

       ESRCH  No thread with the ID thread could be found.

       These functions are provided by glibc since version 2.3.4.

       These functions are non-standard GNU extensions; hence the suffix "_np"
       (non-portable) in the names.

       After a call to pthread_setaffinity_np(), the set of CPUs on which  the
       thread  will  actually  run is the intersection of the set specified in
       the cpuset argument and the set of CPUs actually present on the system.
       The  system  may	 further  restrict the set of CPUs on which the thread
       runs if the "cpuset" mechanism described in cpuset(7)  is  being	 used.
       These  restrictions  on the actual set of CPUs on which the thread will
       run are silently imposed by the kernel.

       These functions are implemented on top of the sched_setaffinity(2)  and
       sched_getaffinity(2) system calls.

       In glibc 2.3.3 only, versions of these functions were provided that did
       not have a cpusetsize argument.	Instead the CPU set size given to  the
       underlying system calls was always sizeof(cpu_set_t).

       A  new  thread  created by pthread_create() inherits a copy of its cre‐
       ator's CPU affinity mask.

       In the following program, the main thread uses pthread_setaffinity_np()
       to  set its CPU affinity mask to include CPUs 0 to 7 (which may not all
       be available on the system), and then calls pthread_getaffinity_np() to
       check the resulting CPU affinity mask of the thread.

       #define _GNU_SOURCE
       #include <pthread.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <errno.h>

       #define handle_error_en(en, msg) \
	       do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)

       main(int argc, char *argv[])
	   int s, j;
	   cpu_set_t cpuset;
	   pthread_t thread;

	   thread = pthread_self();

	   /* Set affinity mask to include CPUs 0 to 7 */

	   for (j = 0; j < 8; j++)
	       CPU_SET(j, &cpuset);

	   s = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
	   if (s != 0)
	       handle_error_en(s, "pthread_setaffinity_np");

	   /* Check the actual affinity mask assigned to the thread */

	   s = pthread_getaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
	   if (s != 0)
	       handle_error_en(s, "pthread_getaffinity_np");

	   printf("Set returned by pthread_getaffinity_np() contained:\n");
	   for (j = 0; j < CPU_SETSIZE; j++)
	       if (CPU_ISSET(j, &cpuset))
		   printf("    CPU %d\n", j);


       sched_getcpu(3),	     sched_setaffinity(2),	sched_setscheduler(2),
       pthread_attr_setaffinity_np(3), pthread_self(3), cpuset(7), pthreads(7)

       This page is part of release 3.22 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at

Linux				  2008-11-27	     PTHREAD_SETAFFINITY_NP(3)

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