Xref: utzoo comp.lang.c:34413 comp.lang.fortran:4230 Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!timbuk!juniper09!ds From: ds@juniper09.cray.com (David Sielaff) Newsgroups: comp.lang.c,comp.lang.fortran Subject: Re: Fortran vs. C for numerical work (SUMMARY) Message-ID: <100916.14288@timbuk.cray.com> Date: 1 Dec 90 07:57:16 GMT References: <9458:Nov2721:51:5590@kramden.acf.nyu.edu> <2392:Nov2902:59:0590@kramden.acf.nyu.edu> <7339@lanl.gov> <6690:Nov3006:15:3890@kramden.acf.nyu.edu> Organization: Cray Research, Inc., Eagan, MN Lines: 32 In article <6690:Nov3006:15:3890@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes: >Several of you have been missing the crucial point. > >Say there's a 300 to 1 ratio of steps through a matrix to random jumps. >On a Convex or Cray or similar vector computer, those 300 steps will run >20 times faster. Suddenly it's just a 15-1 ratio, and a slow instruction >outside the loop begins to compete in total runtime with a fast >floating-point multiplication inside the loop. > >Anyone who doesn't think shaving a day or two off a two-week computation >is worthwhile shouldn't be talking about efficiency. > >In article <7339@lanl.gov> ttw@lanl.gov (Tony Warnock) writes: >> Model Multiplication Time Memory Latency >> YMP 5 clock periods 18 clock periods >> XMP 4 clock periods 14 clock periods >> CRAY-1 6 clock periods 11 clock periods > >Um, I don't believe those numbers. Floating-point multiplications and >24-bit multiplications might run that fast, but 32-bit multiplications? >Do all your matrices really fit in 16MB? On late-model X-MP's and all Y-MP's, those times are correct for 32 bit integer multiplications. The change (from 24 to 32 bit multiplies) corresponds to when the address space on the Cray 1/X-MP/Y-MP line was bumped up from 24 bits to 32 bits (it was always 32 bits on a Cray-2). But this certainly seems to be getting an awfully long way from C ;-) Dave Sielaff Cray Research, Inc. Brought to you by Super Global Mega Corp .com