quoted

+	if (cpu_has_feature(CPU_FTRS_POWER7) && weight == 4) {
    

I think we should avoid using cpu_has_feature like this.  It's better to
create a new feature and add it to POWER7 in the cputable, then check
for that here.

The way that it is now, I think any CPU that has superset of the POWER7
features, will be true here.  This is not what we want.
  

Any ideas for what to call this feature?  ASYM_SMT4 ?

quoted

+	smt_gain /= weight;
    

This results in a PPC div, when most of the time it's going to be a
power of two divide.  You've optimised the divides a few lines above
this, but not this one.  Some consistency would be good.

  

I can turn that into a conditional branch (case statement) with a shift 
for the common 1,2,4 cases which should cover all procs available today 
falling back to a divide for any theoretical future processors that do 
other numbers of threads.