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

[Doug Ledford]

On Wed, 2007-02-14 at 16:29 +0200, Michael S. Tsirkin wrote:
> > Quoting Stefan Roscher <ossrosch at linux.vnet.ibm.com>:
> > Subject: Re: 32-bit build for ppc64 is required
> > 
> > On Wednesday 14 February 2007 14:29, Michael S. Tsirkin wrote:
> > > > Quoting Stefan Roscher <ossrosch at linux.vnet.ibm.com>:
> > > > Subject: 32-bit build for ppc64 is required
> > > > 
> > > > Hi,
> > > > 
> > > > after building the latest ofed build package we recognized that on PPC64 only
> > > > 64-bit libaries were build.
> > > > Because we have customers using older userpace apllications which are
> > > > certified for 32-bit we think additional 32bit support is a requirement for 64bit builds.
> > > > 
> > > > If OFED 1.2 supports 32 bit on ppc64, we have to change the install
> > > > directory.I would suggest to install 32-bit binaries into
> > > > /usr/local/ofed/bin32 directory. So no changes on current naming conventions
> > > > has to be done.The libaries are installed in the /usr/local/ofed/lib directory.
> > > 
> > > The standard practice is to install 64 bit libraries under prefix/lib64
> > > and 32 bit libraries under prefix/lib. Why would PPC64 be any different?
> > 
> > I think you missunderstand my post. The directory for 32/64bit libaries
> > shouldbe prefix/lib and prefix/lib64 respectively. 
> > But current ofed1.2 I saw only prefix/lib64 directory, ie 64bit libs only.  
> 
> Well, this is not by design: AFAIK on x86_64 both types of libraries
> are installed.
> 
> > > I do not think we need 32 bit binaries at all, and there's no other package
> > > I'm aware of that uses "bin32".
> > 
> > We have customers that still use 32-bit userspace applications. 
> > It would be beneficial for them if they can obtain 32bit libs and execs from
> > ofed1.2 in order to run their applications without recompiling them, because
> > for some 32-bit applications recompiling is not an option.
> 
> 32 bit libraries are needed for users to run 32 applications.
> 
> But I still do not see how installing 32 bit binaries alongside the 64
> bit ones is useful, and I do not think other packages provide this option,
> so maybe we shouldn't, either.

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).

-- 
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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