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

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

       #include <linux/getcpu.h>

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

       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       cpu and node is no longer current by the time the call returns.

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

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

       getcpu() was added in kernel 2.6.19 for x86-64 and i386.  Library support
       was added in glibc 2.29 (Earlier glibc versions did not provide a wrapper
       for this system call, necessitating the use of syscall(2).)

       getcpu() is Linux-specific.

       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.

       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.

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

       This page is part of release 5.09 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

Linux                              2019-03-06                          GETCPU(2)