Re: cpu features testing 32 vs 64 bit

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