Hi everybody,
After some google and gcc documentation browsing, I am in the position
of turning to you for some help. Shortly, I am trying to set manually
the branch probabilities with __builtin_expect(), but it seems to me
that it doesn't take the probability I give into account, but it takes
it at most as a hint (CPU: P4, gcc version: 3.3.2). For example, for a
vector a[] with a[i] between 0 and 100, the following code achieves fast
running times for param=0 and param=100 and slower for param=50 instead
of growing linearly with param.
for(i=0;i<n;i++)
if(__builtin_expect(a[i]<param,0) )
j++;
else
j--;
Anything I might have forgot (I compiled the code with -O3)? Any kernel
patch/kernel option/gcc hidden option that would help this thing out?
Thanks,
Gabriel
