Path: utzoo!attcan!uunet!nuchat!sugar!karl From: karl@sugar.UUCP (Karl Lehenbauer) Newsgroups: comp.arch Subject: Dhrystone 2.1 discounts segment thrashing Keywords: integer benchmark Message-ID: <2294@sugar.UUCP> Date: 12 Jul 88 00:42:28 GMT References: <517@pcrat.UUCP> Organization: Sugar Land UNIX - Houston, TX Lines: 36 Readers of the report summarizing Dhrystone benchmark performance of many computers in comp.arch may notice that many machines based on the Intel 80286 performed extraordinarily well in the tests, exceeding the performance of low-end Vaxes, 68000s, etc, and approaching the peformance of 386 machines. This runs strongly counter to my personal experience with these machines. So, why does the 286 perform so well on this "typical C program" benchmark? I think it's because the Microsoft C compiler is getting really good and because the Dhrystone fails to cause any sort of segment thrashing. Readers are directed to the June 1988 issue of (gack) Byte magazine, Table 3 on page 220. In it, the deservedly much-maligned Sieve benchmark is run with varying array sizes. As the array passes the 32K boundary, performance for the 8086 and 80286 declines sharply, while the others continue to increase at a steady rate. An excerpt follows: Array size 20000 40000 Machine (bytes) time (secs) Turbo-Amiga 1.14 2.32 VAX 8600 1.19 2.64 VAX-11/780 3.04 6.38 Amiga 5.68 11.50 VAX-11/750 6.11 13.13 IBM PC AT 8.13 99.71 ^^^^^ I'd like to see a future version of Dhrystone include a something like this, whereby a certain amount of processing of an array is performed for different array sizes, so that the thrashing nature small segmented architectures exhibit when running large programs will be demonstrated. (While the Dhrystone rating for the Mylex 16-Mhz 386/AT replacement motherboard running native-mode 386 Unix is only about three times faster than an 8-Mhz Everex 286 running 286 Unix, timing things such as makes of news and smail have shown the 386 to be nine to ten times faster according to CPU statistics as reported by "time" and by wall time.) -- -- uunet!sugar!karl -- These may be the official opinions of Hackercorp -- I'll have to ask Peter.