NAME | SYNOPSIS | DESCRIPTION | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON
GETCPU(2) Linux Programmer's Manual GETCPU(2)
getcpu - determine CPU and NUMA node on which the calling thread is running
#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.
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.
getcpu() was added in kernel 2.6.19 for x86_64 and i386.
getcpu() is Linux specific.
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there was a very small chance that the returned information would be out of
date.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.
mbind(2), sched_setaffinity(2), set_mempolicy(2), sched_getcpu(3) cpuset(7)
This page is part of release 3.08 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-06-03 GETCPU(2)