getcpu - determine CPU and NUMA node on which the calling thread is running
int getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache);
() 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
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
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
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
(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
is no longer current by the time the call returns.
On success, 0 is returned. On error, -1 is returned, and errno
- Arguments point outside the calling process's address space.
() 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
() 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
intention of getcpu
() is to allow programs to make optimizations with
per-CPU data or for NUMA optimization.
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
(). 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would be out of date.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.