GETCPU(2) Linux Programmer's Manual GETCPU(2)
getcpu - determine CPU and NUMA node on which the calling thread is
int getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache);
Note: There is no glibc wrapper for this system call; see NOTES.
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cpu and node is no longer current by the time the call returns.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.
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.
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information would be out of date.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 argu-
ment is now ignored.
mbind(2), sched_setaffinity(2), set_mempolicy(2), sched_getcpu(3),
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Linux 2017-09-15 GETCPU(2)
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