Re: cpu features testing 32 vs 64 bit

[Pantelis Antoniou <pantelis.antoniou@gmail.com>]

On Friday 09 September 2005 00:02, Becky Bruce wrote:
> So,
>
> in include/asm-ppc64/cacheflush.h is the following:
>
> static inline void flush_icache_range(unsigned long start, unsigned
> long stop)
> {
>          if (!cpu_has_feature(CPU_FTR_COHERENT_ICACHE))
>                  __flush_icache_range(start, stop);
> }
>
> On the 32-bit side, we don't need the feature test -
> CPU_FTR_COHERENT_CACHE is only defined in 64-bit land, and has bits set
> in the upper 32.
>

Oh yes we need it. 8xx is non coherent.

> There's a couple of ways to deal with merging this:
>
> 1) The ever-so-popular #ifdef __powerpc64__around the cpu_has_feature
> test
> 2) No ifdef in the code itself, but #define CPU_FTR_WHATEVER to be 0
> when !__powerpc64__ in cputable.h so that the cpu_has_feature test will
> always fail for 32-bit.
>
> I'd like to get some opinions on this.  Do folks feel like the
> performance hit of doing the compare is enough to justify going with
> method 1?  Should we be using likely/unlikely with the feature test?
>
> This is just one code example - I suspect there will be others as we
> continue the merge, and the importance of performance may differ
> depending on where in the code we are.
>
> Thanks!
> -B
>

Regards

Pantelis