GETCPU(2)						     Linux Programmer's Manual							 GETCPU(2)

NAME

       getcpu - determine CPU and NUMA node on which the calling thread is running

SYNOPSIS

       #include <linux/getcpu.h>

       int getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache);

       Note: There is no glibc wrapper for this system call; see NOTES.

DESCRIPTION

       The getcpu() system call identifies the processor and node on which the calling thread or process is currently running and writes them into
       the integers pointed to by the cpu and node arguments.  The processor is a unique small integer identifying a CPU.  The node  is  a  unique
       small identifier identifying a NUMA node.  When either cpu or node is NULL nothing is written to the respective pointer.

       The third argument to this system call is nowadays unused, and should be specified as NULL unless portability to Linux 2.6.23 or earlier is
       required (see NOTES).

       The information placed in cpu is guaranteed to be current only at the time of the call: unless  the  CPU  affinity  has	been  fixed  using
       sched_setaffinity(2),  the kernel might change the CPU at any time.  (Normally this does not happen because the scheduler tries to minimize
       movements between CPUs to keep caches hot, but it is possible.)	The caller must allow for the possibility that the information returned in
       cpu and node is no longer current by the time the call returns.

RETURN VALUE

       On success, 0 is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       EFAULT Arguments point outside the calling process's address space.

VERSIONS

       getcpu() was added in kernel 2.6.19 for x86_64 and i386.

CONFORMING TO

       getcpu() is Linux specific.

NOTES

       Linux  makes  a	best effort to make this call as fast possible.  The intention of getcpu() is to allow programs to make optimizations with
       per-CPU data or for NUMA optimization.

       Glibc does not provide a wrapper for this system call; call it using syscall(2); or use sched_getcpu(3) instead.

       The tcache argument is unused since Linux 2.6.24.  In earlier kernels, if this argument was non-NULL, then it  specified  a  pointer  to  a
       caller-allocated  buffer  in  thread-local storage that was used to provide a caching mechanism for getcpu().  Use of the cache could speed
       getcpu() calls, at the cost that there was a very small chance that the returned information would be out of date.  The	caching  mechanism
       was considered to cause problems when migrating threads between CPUs, and so the argument is now ignored.

SEE ALSO

       mbind(2), sched_setaffinity(2), set_mempolicy(2), sched_getcpu(3), cpuset(7)

COLOPHON

       This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2013-04-03								 GETCPU(2)