Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!mailrus!nrl-cmf!ames!lamaster From: lamaster@ames.arc.nasa.gov (Hugh LaMaster) Newsgroups: comp.arch Subject: Re: Register Windows (was Re: Japanese...) Message-ID: <16360@ames.arc.nasa.gov> Date: 11 Oct 88 15:29:52 GMT References: <58@zeno.MN.ORG> <91@zeno.MN.ORG> Reply-To: lamaster@ames.arc.nasa.gov.UUCP (Hugh LaMaster) Organization: NASA Ames Research Center, Moffett Field, Calif. Lines: 45 In article <9837@cup.portal.com> bcase@cup.portal.com writes: >John Danskin at decwrl writes: (the stupid portal mailer doesn't include >>By the way: >> There is a paper: [from Berkeley] >> Which shows that the MIPS R2000 (aside from running faster) achieves >> fewer memory references (in almost all cases) than SPARC with all >> levels of optimization and as many as 7 register windows. >Well, this is news to me! I must blush and appologize for many of my >past postings if these results are true for architectures like the 29K. >I do hope they included the effects of high-bandwidth, sequential-access >memories. > > > > > > > I wonder what that paper is. There is another paper which may be of interest: Look in the September 1987 IEEE Computer, "And Now a Case for More Complex Instruction Sets", IEEE Computer, Sept. 87, Vol. 20, No. 9, pages 71-83. This paper makes the case, again, that you need to simulate and test, not hypothesize, what the effects of the various optimizations are. However, while we are hypothesizing, the results of the paper again call into question the efficacy of register windows. For example: "From data traffic considerations alone, it seems that OBI360 [a particular 1 address instruction format looked at in the paper] with a register set of about size 16 plus a small data cache is preferable to multiple register sets for most area combinations..." [page 83] How about someone publishing a simulation showing the results of using lazy windows? -- Hugh LaMaster, m/s 233-9, UUCP ames!lamaster NASA Ames Research Center ARPA lamaster@ames.arc.nasa.gov Moffett Field, CA 94035 Phone: (415)694-6117