🚀 go-pugleaf

>On 2 May 91 16:29:09 GMT, lamaster@pioneer.arc.nasa.gov (Hugh LaMaster) said:

Hugh> I have only limited experience with the new, fast-only-in-cache,
Hugh> machines, but I have to say that the code you need to get
Hugh> optimum performance is even more non-intuitive than that for the
Hugh> older vector architecture machines.

That is absolutely true, and a serious problem for those of us
concerned about performance.  I found it very easy to optimize code
for the Cyber 205 and ETA-10 (if you use long vectors, then just write
simple DO loops, otherwise migrate to another platform!).  It is a
little bit harder on the Cray X&Y (mostly because there are so many
more codes that it is *possible* to optimize), and it is pretty
difficult on Cray 1, Cray 2, and cached killer micros.  Techniques
like "unroll outer loop and jam resulting inner loops" are great in
theory, but all too often I find that the various machine's
optimizers require *slightly* different code --- there is no one piece
of code (even a nice block-mode version) that optimizes well on a
broad range of scalar platforms....  Matrix multiply is a good example
of this: the code that is required to run at peak speeds on an RS/6000
does not run particularly well on a MIPS.  A slightly different style
of source optimization is required there....
--
John D. McCalpin			mccalpin@perelandra.cms.udel.edu
Assistant Professor			mccalpin@brahms.udel.edu
College of Marine Studies, U. Del.	J.MCCALPIN/OMNET