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node is no longer current by the time the call returns.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.
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would be out of date.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 3.74 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
http://www.kernel.org/doc/man-pages/.
