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.