[openib-general] 32-bit build for ppc64 is required

[Doug Ledford]

On Thu, 2007-02-15 at 07:57 +0200, Michael S. Tsirkin wrote:

> > The choice of 32/64 bit default is done on a per arch basis.  With
> > x86_64/i386, the increased number of CPU registers in 64bit mode
> > outweighs the increased code bloat that goes along with 64bit mode.  On
> > PPC, no such register benefit exists for 64bit mode.  As such, 32bit
> > apps on PPC are faster than the equivalent 64bit apps up to the point at
> > which a 4GB address space becomes a problem.  Correspondingly, the
> > default binaries on PPC are 32bit, and only those that *need* to be
> > 64bit are.  While a customer's application may need >4GB address space,
> > certainly all the ibutils, diags, opensm, etc. do not.  As a result, we
> > compile all of those utilities as 32bit by default on PPC.  We also ship
> > all the libs as both 32/64bit so users can select the appropriate
> > environment for their particular application (with the exception of
> > dapl, which doesn't support 32bit and for which I filed a bug around the
> > time of OFED 1.1).
> 
> So, what you suggest is - build 2 types of libraries, but on PPC make
> binaries 32 bit? That's easy - do others agree to this approach?

Yep, that's what we do.

> Another option is to build binaries with whatever type of binary
> gcc without extra flags generates by default.

Usually this should work, but I don't rely on that since we also support
s390/s390x (although not with Infiniband, but the OpenMPI alternative
that we shipped with RHEL4, lam, gets compiled on s390/s390x) and that
pair is a bit of an odd mix and I don't have one setting here at my
house where I work, so it's hard for me to confirm that just leaving
things to happen by default works as anticipated.  If they would ever
make an s390 that uses less than a gigawatt of power and heats less than
a large sized convention center, that could change... ;-)

-- 
Doug Ledford <dledford at redhat.com>
              GPG KeyID: CFBFF194
              http://people.redhat.com/dledford

Infiniband specific RPMs available at
              http://people.redhat.com/dledford/Infiniband
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