Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!dcl-cs!aber-cs!athene!pcg From: pcg@cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.arch Subject: Re: Kneejerk answers to Herman Message-ID: Date: 10 Feb 91 17:37:04 GMT References: <27AF17B9.72E2@tct.uucp> <5275@mentor.cc.purdue.edu> <27B19A39.321E@tct.uucp> <1991Feb9.004131.5977@murdoch.acc.Virginia.EDU> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 41 Nntp-Posting-Host: odin In-reply-to: gl8f@astsun7.astro.Virginia.EDU's message of 9 Feb 91 00:41:31 GMT On 9 Feb 91 00:41:31 GMT, gl8f@astsun7.astro.Virginia.EDU (Greg Lindahl) said: gl8f> In article <27B19A39.321E@tct.uucp> chip@tct.uucp (Chip gl8f> Salzenberg) writes: chip> Machines have been designed for efficient execution in the most chip> common cases. If the most common cases are compiled C and Fortran chip> programs, optimizing the hardware for those cases is only natural. chip> Remember, Herman, your instruction mix is radically atypical. gl8f> Actually, C and Fortran programs show a wide variety of "common gl8f> cases". Algorithms change, and so does the optimal hardware. gl8f> Example: 2 years ago my "typical" hydrodynamics code almost never gl8f> did a square root. Now it does quite a lot of them. Had you gl8f> designed your instruction set back then, and your competition gl8f> covered their asses by slowing themselves down a little bit to gl8f> provide good performance in a wider variety of situations. [ ... ] gl8f> Optimize the common case, but cover your ass. An architect! Incredible! On these screens! From the USA (East Coast, though :->), too! Somebody who actually realizes that things that change with time and variability is the rule, not the exception! Somebody who is willing to pay a small price on the 80% to get a large gain on the 20%! I think that this posting sums up a lot of the discussions about architecture we have been having here. Architecture, whether about boundaries between hardware layers, or software ones, or the boundary between the two, is about the sort of things described above. And taking very well reasoned bets. Well, I hope the Imperial MITI DRAM Service does not put you on their hit list :-). -- Piercarlo Grandi | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcsun!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk