Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!cornell!uw-beaver!blake!lgy From: lgy@blake.acs.washington.edu (Laurence Yaffe) Newsgroups: comp.arch Subject: Re: SPARC vs. MIPS on gcc Summary: When is block refill better? Message-ID: <486@blake.acs.washington.edu> Date: 4 Jan 89 00:28:54 GMT References: <10436@winchester.mips.COM> Reply-To: lgy@blake.acs.washington.edu (Laurence Yaffe) Organization: University of Washington, Seattle Lines: 50 In article <10436@winchester.mips.COM> mash@mips.COM (John Mashey) writes: [[Much stuff about benchmarking deleted]] -Some of the more extreme MIPS pairwise combinations -get up around a 1.3X variation (for example, M/2000 versus M/1000): - if a benchmark has a low cache miss rate, the ratio is close to - the clock-rate difference. - if a benchmark has a high data cache miss rate, and block-fetch - works, the 2000 is better than the 1000 by more than the - clock rate. - if a benchmark has a high data cache miss rate, and block-fetch - DOESN'T work (compress is the notorious example), then - a 2000 is not as much better as the clock-rate difference. - (Compress is notorious because it hashes data into a huge - sparse array & 1-word-refilled data caches are BETTER - than N-word-refilled caches, which is not often true.) ^^^^^^^^^^^^^^^^^^^^^^^ I'm curious about the basis for this judgement. In much of my own recent work, I've been dealing with several large, integer programs which do special purpose symbolic algebra. Much of the execution time of these programs is devoted to searches in a large ordered hash table (~50 Kb), plus assorted string operations which typically only access the first few characters in a string. These appear to be examples of programs for which multi-word data cache refill is not helpful. For example, comparing a MIPS M/120 (16.7 MHz) versus a 20 Mhz M/2000, I've found: Program #1 ("obsgen") MIPS M/120 (-O2) 821 sec MIPS M/2000 (-O2;3.10) 795 Program #2 ("scrgen") MIPS M/120 (-O2) 808 sec MIPS M/2000 (-O2;3.10) 826 Obviously, these two programs may not be representative of "typical" programs (whatever those are). However, I would not be surprised if many "data-management" type programs (with large hash tables, binary trees, etc.) have similar behavior - namely better performance with single word data cache refill. -john mashey DISCLAIMER: -UUCP: {ames,decwrl,prls,pyramid}!mips!mash OR mash@mips.com -DDD: 408-991-0253 or 408-720-1700, x253 -USPS: MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086 -- Laurence G. Yaffe Internet: lgy@newton.phys.washington.edu Department of Physics, FM-15 or: yaffe@phast.phys.washington.edu University of Washington Bitnet: yaffe@phast.bitnet Seattle WA 98195