Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!julius.cs.uiuc.edu!ux1.cso.uiuc.edu!ux1.cso.uiuc.edu!aglew From: aglew@crhc.uiuc.edu (Andy Glew) Newsgroups: comp.arch Subject: Re: Alignment on RS/6000 Message-ID: Date: 20 Nov 90 07:45:34 GMT References: Sender: news@ux1.cso.uiuc.edu (News) Organization: Center for Reliable and High-Performance Computing University of Illinois at Urbana Champaign Lines: 21 In-Reply-To: aglew@crhc.uiuc.edu's message of 19 Nov 90 21:29:26 I'll bet the misalignment slowdown noted in the last post was due to trapping and handling the misalignment in the trap handler. But it makes you think: is it really worth being backward compatible if there is such a huge performance penalty? Can you imagine the novice user who would not know how to look for such a problem? Can you imagine UNIX Review publishing a benchmark with that sort of problem? Put another way, maybe such backward compatibility should not be present by default. Maybe the program should die with the message Error: misaligned accesses. "fort -misaligned" may be used. so that the user would have to go and turn on the misaligned compatbility mode, and would be aware of the possible performance costs. -- Andy Glew, a-glew@uiuc.edu [get ph nameserver from uxc.cso.uiuc.edu:net/qi]