getcpu2

Usage

#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <sched.h>

Library

Standard C library (libc, -lc)

Overview

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 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 The caller must allow for the possibility that the information returned in cpu and node is no longer current by the time the call returns.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 to indicate the error.

Errors

EFAULT

Arguments point outside the calling process's address space.

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.