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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);

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.

       The  information  placed  in cpu is only guaranteed to be current 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
       be  prepared  to  handle the situation when cpu and node are no longer the current CPU and
       node.

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       information would be out of date.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 3.35 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.