Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!udel!nigel.ee.udel.edu!mccalpin From: mccalpin@perelandra.cms.udel.edu (John D. McCalpin) Newsgroups: comp.arch Subject: Re: RISC vs. CISC -- SPECmarks Message-ID: Date: 3 May 91 13:15:30 GMT References: <3423@charon.cwi.nl> <11602@mentor.cc.purdue.edu> <1991Apr30.163153.18568@midway.uchicago.edu> <1991May2.162909.9165@news.arc.nasa.gov> Sender: usenet@ee.udel.edu Organization: College of Marine Studies, U. Del. Lines: 26 Nntp-Posting-Host: perelandra.cms.udel.edu In-reply-to: lamaster@pioneer.arc.nasa.gov's message of 2 May 91 16:29:09 GMT >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