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* uncachedev: mmap memory that is not cached by CPUs2013.1archived-2013.1Glenn Elliott2013-08-07
This patch creates a new character device, uncachedev. Pages of RAM allocated by this device are not cached by CPUs. Uses for such pages: 1) Determining *very* pessimistic emperical worst- case execution times. 2) Compare against performance with caches (quantify the avg. case benefit). 3) Deterministic memory accesses (access cannot cause a cache eviction.) 4) Theoretically, increased performance can be achieved by storing infrequently accessed data in uncache pages. uncachedev allocates pages with the pgprot_noncached() page attribute for user applications. Since pages allocated by uncachedev are not locked in memory by default, applications with any access level may mmap pages with uncachedev. Limitations: 1) Uncache pages must be MAP_PRIVATE. 2) Remapping not supported. Usage (user level): int size = NR_PAGES*PAGE_SIZE; int fd = open("/dev/litmus/uncache", O_RDWR); char *data = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0); <...do stuff...> munmap(data, size);