Re: [PATCH 2/2] powerpc: implement arch_scale_smt_power for Power7

Joel Schopp
2010-01-20T22:09:43Z

>> + 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 ?
>
>> + 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.