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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);
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