/* * On multiprocessor systems we can gain an improvement in performance * by being mindful of which cachelines data is placed in. * * __read_mostly: * * It makes sense to ensure that rarely modified data is not * placed in the same cacheline as frequently modified data. * To mitigate the phenomenon known as "false-sharing" we * can annotate rarely modified variables with __read_mostly. * All such variables are placed into the .data.read_mostly * section in the kernel ELF. * * Prime candidates for __read_mostly annotation are variables * which are hardly ever modified and which are used in code * hot-paths, e.g. pmap_initialized. * * __cacheline_aligned: * * Some data structures (mainly locks) benefit from being aligned * on a cacheline boundary, and having a cacheline to themselves. * This way, the modification of other data items cannot adversely * affect the lock and vice versa. * * Any variables annotated with __cacheline_aligned will be * placed into the .data.cacheline_aligned ELF section. */