title: When should we use prefetch?
body: <p>Some CPU and compilers supply prefetch instructions. Eg: __builtin_prefetch in <a href="http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html" rel="nofollow noreferrer">GCC Document</a>. Although there is a comment in GCC's document, but it's too short to me.</p>
  <p>I want to know, in practice, when should we use prefetch? Are there some examples?</p>