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
The processor is a unique small integer identifying a CPU.
The node is a unique small identifier identifying a NUMA node.
is NULL nothing is written to the respective pointer.
The third argument to this system call is nowadays unused.
The information placed in
is only guaranteed to be current at the time of the call:
unless the CPU affinity has been fixed using
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
are no longer the current CPU and node.
was added in kernel 2.6.19 for x86_64 and i386.
is Linux specific.
Linux makes a best effort to make this call as fast possible.
The intention of
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
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
Use of the cache could speed
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the returned information would be out of date.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.