[ccp4bb]: Some naive questions about AltiVec

[Derek Logan <derek.logan@mbfys.lu.se>]

***  For details on how to be removed from this list visit the  ***
***          CCP4 home page http://www.ccp4.ac.uk         ***

Hi there,

Given the amount of enthusiasm out there for Mac OS X and the recent 
discussion of benchmarks, I was wondering if anyone had attempted to 
optimize CCP4 code for the G4 processor, in particular to exploit the 
AltiVec/Velocity Engine. It seems to me that unless one attempts to 
exploit these inbuilt features, the G4 is always going to be a bit of a 
lame duck compared to AMD or Intel processors and one will only use Macs 
because of the beauty of the operating system! From reading, e.g.

http://gravity.psu.edu/~khanna/autovp.html

I get the impression that the untapped potential for speed enhancements 
is pretty large. Also, here is an excerpt from a NASA study on 
computational fluid dynamics (accessible through the Web page above):

"Results indicate that the PowerMac G4 system has the capacity to be an 
inexpensive high performance scientific computing platform. Much of that 
potential is currently unrealized, however, due to the limited amount of 
AltiVec support in FORTRAN. Without the parallel vector processing 
capabilities of AltiVec, the G4 places near the end of the pack in 
preformance tests using standard FORTRAN scientific codes. In limited 
cases where AltiVec acceleration was available and tested under FORTRAN, 
the G4 showed a clear advantage, with 4-7x greater performance and a 
5-8x greater cost effectiveness than all other workstations evaluated. 
Examples presented in this report show that only minor re-coding would 
be necessary to implement AltiVec instructions if they were accessible 
to standard FORTRAN programming."

The problem is that there only seems to be one automatic vectorization 
program, i.e. VAST from Veridian. The combined FORTRAN/C optimizer costs 
$1000! Absoft bundle VAST for FORTRAN with their ProFortran compiler for 
$1300. This is obviously a bit much for an individual lab, so I wondered 
if the CCP4 developers, or any other developers and implementers out 
there, had thought about this issue. Obviously it means producing major 
amounts of tailor-made code for a specific operating system, which is 
maybe not true to the CCP4 philosophy.

Regards
Derek
--
Derek Logan             tel: +46 46 222 1443
Associate professor     fax: +46 46 222 4692
Molecular Biophysics    	
Lund University
Box 124, Lund, Sweden