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       in cpu and node is no longer current by the time the call returns.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 as possible.  (On some architectures, this is done
       via an implementation in the  vdso(7).)   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), vdso(7)

COLOPHON

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