Path: utzoo!attcan!uunet!tank!ncar!asuvax!cs.utexas.edu!rice!uw-beaver!Teknowledge.COM!unix!garth!fouts@bozeman.ingr.com (Martin Fouts) From: fouts@bozeman.ingr.com (Martin Fouts) Newsgroups: comp.sys.super Subject: Re: Cray tidbits Message-ID: <390@garth.UUCP> Date: 31 May 90 16:28:07 GMT References: <354@garth.UUCP> <1990May23.041119.4359@ux1.cso.uiuc.edu> Sender: fouts@garth.UUCP Distribution: comp Organization: INTERGRAPH (APD) -- Palo Alto, CA Lines: 97 In-reply-to: klietz@ux1.cso.uiuc.edu's message of 23 May 90 04:11:19 GMT In article <1990May23.041119.4359@ux1.cso.uiuc.edu> klietz@ux1.cso.uiuc.edu (Alan Klietz) writes: From: klietz@ux1.cso.uiuc.edu (Alan Klietz) Summary: Be not hasty to judge Aw, Marty don't write off CRI too fast. While I admit that my sentiments about the YMP 2E are probably similar to yours, viz. divergence from CRI's strengths into areas of weakness, etc., they will survive based on outstanding technical merit (as usual), but in other areas. CRI's outstanding technical merit walked out the door, packed his bags, and went to Boulder. (;-) What areas? Data parallelism, I think. I am seeing deja-vu in the acceptance of the scientific computing community to DP as I saw in the acceptance to UNIX back in the mid-80's (cf. ETA discussion). Those entities that embrace and push DP fastest will be the winners, while those that that continue with big iron vector boxes will be crushed by the Killer Micros and go the way of NOS Cybers and AOS Novas. Data parallelism is an easy way to solve easy to parallelize problems. It is a poor way to solve hard to parallelize problems. As example, I cite that the CM compilers do not run on the CM... [Of course, most of the problems in the "scientific computing" community are 'easy', so that may not be an important point. Linear algrabra exhibits good locality of reference and relative independence of calculations.] CRI has embraced DP in a big way in only the last few months, I think. I have a pretty good idea, based totally on supposition, on what the teraflop YMP will look like (hint: think CM.) I hope it isn't in the same big way they embraced "network supercomputing" --- claiming to have invented something which on analysis only means what other people call 'interconnectivity.' If that's true, they'll introduce a PARDO construct to Fortran and call it data parallelism. (;-) I'm not selling my CRI stock anytime soon. Me either. I can't get the money I put into it back, and I don't need the loss on my taxes. (:-( [CRI is now trading ~47, or about half the average cost of CRI stock...] But seriously. For data parallelism to be fully effective one needs a very high bandwidth low latency intercnonnect mechanism and problems which exhibit high locality of reference. The power of the processing element isn't very important by comparison. A large part of Thinking Machine's success with the SIMD approach in the connection machine as opposed to the price competitive MIMD approach of "hypercube" systems is the very clever and rather quick routing of the machine, coupled with the very low synchronization cost built into the lock step approach of SIMD. Hillis, in his PHD thesis, argues that the qualitative value of data parallelism only comes when a very large number of processing elements can be effectively utilized in parallel. CRI can build a data parallel machine in one of two ways. It can build a medium number of processor MIMD machine with near zero synchronization cost and use the medium number of processors to model the large number of processors Hillis postulates. Or, it can build a large number of processor systems. In either case, doing this with a MIMD system is a very difficult technical problem because of the cost of synchronization. CRI could possibly build a SIMD implementation of the Y/MP; that is a Y/MP instruction set driven data parallel processor. There are only three things needed to do this that they don't currently have the expertise for: 1) hardware 2) software 3) marketing (;-) In fact, I can't even imagine such a machine running. However, I've been wrong about enough things that I'll try instead to imagine how long it will take Crayless-Cray to produce the machine. Let's see the C90 project has to be done first and then people freed up.... (think, think, gaze at crystal ball:) It would take CRI at least 10 years from today to introduce a usable SIMD system ala connection machine with a processor count in the low to medium thousands. Can they survive that long without a follow on to the Y/MP, which will be obsolete in 1994, if current industry trends of five year life times are followed? Marty -- Martin Fouts UUCP: ...!pyramid!garth!fouts ARPA: apd!fouts@ingr.com PHONE: (415) 852-2310 FAX: (415) 856-9224 MAIL: 2400 Geng Road, Palo Alto, CA, 94303 If you can find an opinion in my posting, please let me know. I don't have opinions, only misconceptions.