|GETCPU(2)||Linux Programmer's Manual||GETCPU(2)|
int getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache);
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 The caller must allow for the possibility that the information returned in cpu and node is no longer current by the time the call returns.
- Arguments point outside the calling process's address space.
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cache could speed getcpu() calls, at the cost that there was a very small chance that the returned information would be out of date.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.