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From: tim@amdcad.AMD.COM (Tim Olson)
Newsgroups: comp.lang.c
Subject: Re: Dhrystones
Message-ID: <19425@amdcad.AMD.COM>
Date: Thu, 3-Dec-87 19:38:29 EST
Article-I.D.: amdcad.19425
Posted: Thu Dec  3 19:38:29 1987
Date-Received: Tue, 8-Dec-87 00:59:08 EST
References: <3368@rosevax.Rosemount.COM> <5096@ccv.bbn.COM>
Reply-To: tim@amdcad.UUCP (Tim Olson)
Organization: Advanced Micro Devices
Lines: 27
Keywords: C, performance, useful

In article <5096@ccv.bbn.COM> kgregory@ccv.bbn.com.BBN.COM (Keith D. Gregory) writes:
| In article <3368@rosevax.Rosemount.COM> richw@rosevax.Rosemount.COM (Rich Wagenknecht) writes:
| >Could somemone tell me what a 'Dhrystone' (<-sp.?) is?
| >Why is it used so often to evaluate compiler performance?
| >Is it a good overall indicator of compiler peformance?
|
| 1 - Compare different compilers for a given machine.  I find this to be very
|     useful - although there are certainly many factors contributing to the
|     efficiency of compiled code, I've found that Dhrystone figures give a
|     fairly accurate comparison of two compilers (as I see it, if a compiler
|     writer makes efficient integer procesing code, the system calls will
|     probably be efficient too).

I just wanted to add the caveat that Dhrystone has some major problems
as a benchmark when you are talking about very good optimizing
compilers.  There exists quite a lot of "dead code" in Dhrystone
(expressions which aren't ever used) which good compilers can optimize
totally away.  This isn't the case with real-world code.  At the
high-end, all you are comparing with Dhrystone is how much code your
compiler threw away vs another compiler ;-)

Dhrystone is also heavily weighted towards string operations (strcpy &
strcmp can total 35% - 40% of the runtime).

	-- Tim Olson
	Advanced Micro Devices
	(tim@amdcad.amd.com)