Hi all,
There is a lot of "if statement" in system, and GCC provides a
feature,"__builtin_expect", which let compilers know which branch is
mostly run. as we known, miss-prediction will lead the performance
lost(because the CPU will thrown away some instructions, and re-fetch some
new instructions). so that we can tell GCC how produce more efficient code.
for example as following.
It will gain performance promotion i think. As i know, the in Linux kernel,
this feature is also applied already.
#define likely(cond) __builtin_expect(cond,true)
#define unlikely(cond) __builtin_expect(cond,false)
if (likely(cond)) {
//most likely run.
xxxx
} else //otherwise.
{
xxxx
}
Best Regards.
Hom.
