__BUILTIN_PREFETCH(3) | Library Functions Manual | __BUILTIN_PREFETCH(3) |
In addition to addr, there are two optional stdarg(3) arguments, rw and locality. The value of the latter should be a compile-time constant integer between 0 and 3. The higher the value, the higher the temporal locality in the data. When locality is 0, it is assumed that there is little or no temporal locality in the data; after access, it is not necessary to leave the data in the cache. The default value is 3. The value of rw is either 0 or 1, corresponding with read and write prefetch, respectively. The default value of rw is 0. Also rw must be a compile-time constant integer.
The __builtin_prefetch() function translates into prefetch instructions only if the architecture has support for these. If there is no support, addr is evaluated only if it includes side effects, although no warnings are issued by gcc(1).
while (mlen >= 32) { __builtin_prefetch(data + 32); partial += *(uint16_t *)data; partial += *(uint16_t *)(data + 2); partial += *(uint16_t *)(data + 4); ... partial += *(uint16_t *)(data + 28); partial += *(uint16_t *)(data + 30); data += 32; mlen -= 32; ...
Ulrich Drepper, What Every Programmer Should Know About Memory, http://www.akkadia.org/drepper/cpumemory.pdf, November 21, 2007.
December 22, 2010 | NetBSD 7.2 |