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  mini‐
       mize  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  cur‐
       rent 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 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2013-04-03                                  GETCPU(2)