[daip] aips on linux/amd64, multihost site

[Eric Greisen]

Vincent McIntyre writes:
 > We have some sparc and some i[3456]86 machines, in separate sites
 > (because of the endianness differences in the AIPS on-disk data formats).
 > All share the same $AIPS_ROOT, otherwise. This works well.
 > 
 > We are now considering putting in some amd64 machines.
 > However the install.pl script appears not to distinguish i386 and amd64,
 > in the sense that it sets $ARCH="LINUX" for both. So if I understand
 > correctly, if one were to try to build AIPS from source on an amd64 
 > machine, for the same site as the i386 installation, this action would
 > overwrite the existing binaries for i386.
 > 
 > The questions:
 > 
 > 1. Is it a supported configuration to run linux i386 binaries on amd64?
 >     I'm expecting "no" but thought I should ask to be sure.

        Actually this works fine.

 > 
 > 2. Assuming we set up amd64 binaries in a separate site, would it be
 >     possible to access AIPS data files from both i386 and amd64 hosts,
 >     without corrupting the data files? The data files would be accessed
 >     over NFS.

         The formats are identical including byte order.  But separate
sites means no normal access.

 > 
 > 3. While I was looking into this I noticed there was no simple listing
 >     of "supported architectures" on the website[1] aside from [2] which
 >     doesn't mention amd64.
 >     Is it worth reworking [2] as a bullet-list (derived from install.pl)?
 >     It might be better to break that list out into a separate file (eg [3])
 >     and just linking to it from the current release info file (ie [2]).
 > 

I don't really view the AMD64 as separate.  The Linux binaries that we
ship are linked/optimized for 3 architectures and run faster on
amd64's than the older GNU executables even when built for the 64-bit
architecture.  The latest gfortran seems to have made up this 7%
difference, but treating AMD64 as really different does not seem
necessary.  My recommendation - do not separate the amds to another
site and use our binary install.  I suppose that curtails local AIPS
software development, but do you still do that?  I know you once did,
but we have worked to reduce the need for that I thought to zero -
unless you have new/different tasks not ported to us.

Eric Greisen