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From: steven@cwi.nl (Steven Pemberton)
Newsgroups: comp.sys.atari.st,comp.sys.misc,comp.sys.amiga
Subject: Re: Weighty instructions
Message-ID: <94@piring.cwi.nl>
Date: Tue, 20-Oct-87 06:06:50 EDT
Article-I.D.: piring.94
Posted: Tue Oct 20 06:06:50 1987
Date-Received: Wed, 21-Oct-87 06:36:28 EDT
References: <1138@water.waterloo.edu> <2452@cbmvax.UUCP> <7422@e.ms.uky.edu> <90@piring.cwi.nl> <557@rover.UUCP>
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Organization: CWI, Amsterdam
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Xref: mnetor comp.sys.atari.st:5799 comp.sys.misc:938 comp.sys.amiga:9641

In article <557@rover.UUCP> mph@rover.UUCP (Mark Huth) writes:
> It seems to me that if one programs in C, then the C compiler is part
> of the environment.  The fact that the compiler distorts the raw
> machine power to some extent is true, but unless you are an assembly
> guru [...] you cannot generate code to fully utilize a giver
> archetecture'r power.  Therefore, the high-level language benchmarks
> are very useful.
> 
> We are able to improve the Dhrystone ratings of our systems by as much
> as 33% by improving the compiler.  This is real good news, as all
> programs get some considerable performance gain by recompilation as
> better compilers become available.

Well, this is exactly what I meant. The problem with a MIPS rating is
that you know little about what sort of instructions are involved. At
least a Dhrystone rating gives you an objective number, but it is
still not a completely good indication of pure machine power because
the compiler distorts the figure (although it does at least give a
lower bound). Just look at the figures for different C compilers on
different makes of 8 MHz 68000: they run from 330 to 1370! The fact
that you could tune your compiler to give 33% better performance only
goes to show that the Dhrystone figure is only loosely related to the
machine performance.

Steven Pemberton, CWI, Amsterdam; steven@cwi.nl