Re: Adding cache shape info to powerpc

[Steven Munroe <munroesj at linux dot vnet dot ibm dot com>]

On Fri, 2016-12-02 at 07:10 +1100, Benjamin Herrenschmidt wrote:
> On Thu, 2016-12-01 at 09:10 -0600, Steven Munroe wrote:
> > > The old format was only used by other architectures, not powerpc, do I
> > > still need to pick different numbers in that case ?
> > > 
> > > As for IFUNC I don't think so but I'll let Steve reply as I believe he
> > > is the original requestor for the functionality.
> > > 
> > 
> > Ben were are we on this? 
> > 
> > This is needed to fix a customer reported bug for lack of
> > sysconf(_SC_*CACHE_SIZE) support on powerpc.
> > 
> > Adding this information to the cputable and then auxv fits into the
> > current sysconf infrastructure best.
> > 
> > When we know the AT_ info format and upstream Kernel version we can
> > update kernel-features.h and enable a sysconf.c fragment to return these
> > values for powerpc 
> 
> I was waiting for a review by you guys to tell me what you want in the
> AT_* entries. People weren't too happy with my first sketch that used
> the same entries used by a couple of other archs but with a slightly
> different format.
> 
> Once we agree on an encoding/format I can resend the patches.

The AT_*_CACHESHAPE where encoding more information then strictly
required for _SC_*CACHE_SIZE.

So the alternative is to define 4 new/different AT_*_CACHESIZE entries
where each is just the respective cache size in KB.

This should handle current and projected values in 32-bits for the
foreseeable future. 

Thanks