AIPS on an ALPHA AXP Clone (Linux)

[Patrick P. Murphy]

Normally AIPS memos are not sent via email or usenet, but this one is
small enough and (in my opinion) of sufficient interest to justify an
exception.  

			       AIPS Memo 96

			AIPS on an ALPHA AXP Clone

       Robert L. Millner, Patrick P. Murphy, and Jeffrey A. Uphoff
		   National Radio Astronomy Observatory
		      Charlottesville, Virginia, USA

			     October 9, 1997

ABSTRACT

    There has been some interest, both within NRAO and in the general
    Radio Astronomy Community, in the possibility of running AIPS on
    one of the many "clone" systems based on the Digital ALPHA AXP
    21164 processor.  Recently, NRAO/Charlottesville acquired such a
    system and proceeded to install the Linux operating system
    thereon.  We have also started the process of porting AIPS to this
    64-bit system, though the results reported herein are based solely
    on the use of binaries generated on an OSF/1 (Digital Unix) ALPHA
    processor and copied to the Linux system.  We have successfully
    run the "DDT" suite of programs on this Linux/Alpha system and
    have achieved an AIPSMark(93) of 9.0. 


INTRODUCTION --- The Porting

The Alpha clone in question is an Aspen Durango with 64 Megabytes of
memory, 1 Megabyte of L3 cache, a 433MhZ 21164 Alpha AXP processor, a
Quantum Fireball 6 GByte IDE disk, and a CMD646 PCI IDE controller.
In addition, a Buslogic BT948 SCSI-II card was borrowed for the tests,
as was a Quantum XP34550S Fast SCSI-II disk.  This system is running a
development kernel (Linux 2.1.57) based on a standard Red Hat
installation.

Porting AIPS to such a system is problematic.  Under Linux, the
approach in the past has been to use the GNU gcc compiler and f2c
Fortran-to-C converter combination, but our initial forays into this
realm revealed 64-bit problems with the f2c converter (i.e., it was
not 64-bit clean).  The second approach considered was to use the
newer g77 compiler, but this was deferred on the basis of our
experience with a separate porting attempt on an Intel/Linux system:
it compiles but fails in the Q routines with a segmentation fault.

However, one of the nicer features of Linux on the ALPHA architecture
is that statically linked binaries generated on an OSF/1 "Digital
Unix" system can be made to run under Linux/Alpha.  After verifying
this was the case, we proceeded to build a set of such static binaries
for AIPS on one of our DEC Alpha systems, compiling with Digital Unix
f77 and cc using optimizations and tuned for the 21164 processor.
Such binaries turn out to be quite large, tipping the scales at over
500 Megabytes for the LOAD area.  It may be possible to reduce these
via stripping, and we are investigating the possibility of linking in
shared mode to the system libraries on the OSF/1 system.  There are
both technical and licensing issues to be overcome for this to work.


Testing and Results

Details of the "DDT" certification and benchmarking package are
covered in AIPS memo 85 and will not be repeated here.  Suffice it to
say that the LARGE version of the DDT was run on the system in
question, using the standard methods as described in aforesaid memo.

The system was first tested with the IDE disks.  When these were
"un-tuned" the resulting AIPSMark(93) is 4.2.  Using the system hdparm
to tune the disk to "-m 16 -c 1 -u 0" increases this value to 4.5 but
has the unfortunate side effect of rendering the machine unusable for
anything else.  Tuning it with "-m 8 -c 1 -u 0" gets a 4.5 also, and
the CPU actually has some idle time and can be used although sluggish
and unresponsive.  Un-masking IRQs brings the system back down to
un-tuned performance but makes it more usable.

However, when the swap, /tmp and AIPS areas (source and data) are
moved to the SCSI drive, there is a dramatic improvement.  On an
otherwise unloaded system, the AIPSMark(93) shoots up to 9.0.  If
there is some background activity (reading e-mail, running a web
browser, etc.), the result slows down to 8.6.  The system "top"
utility reports consistently less than 5% idle time and under 8% used
by the system with the rest going almost exclusively to AIPS tasks.
The disk needed no tuning.

Finally, for some idea of how well these binaries would perform under
OSF/1, they were run on a Digital Alphastation with a 400MHz 21164
processor, which was running Digital Unix version 4.0.  These binaries
were accessed via NFS, but everything else (the data areas
specifically) was local.  The AIPSMark(93) for this test on an
otherwise unloaded system was 10.0.  This would seem to indicate that
the emulation code under Linux on the Alpha has relatively little
overhead.


Conclusions

The viability of a generic Alpha "clone" with Linux as an operating
system for AIPS has been demonstrated.  The approximate cost of such a
system is on the order of US$5k and the dollar-per-AIPSMark(93) value
of circa $600 is perhaps the lowest value determined by the authors to
date.  The use of a good SCSI controller and disk moved the machine
out of the desktop PC arena and into the mid- to high-performance
workstation arena.

Further investigation will no doubt continue into this system,
especially in the areas of native Fortran compilers or emulators.
However, NRAO now has the ability to provide the Radio Astronomical
community with software that will run at high performance levels on
relatively low cost hardware.

-- 
  \|/  ____  \|/   Pat Murphy; email http://orangutan.cv.nrao.edu/kippure.html
   @  / oO \  @       Plan, PGP, Pages: http://orangutan.cv.nrao.edu/plan.html
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