Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!mash
From: mash@mips.com (John Mashey)
Newsgroups: comp.benchmarks
Subject: Re: Which benchmarks are useless?
Message-ID: <3054@spim.mips.COM>
Date: 4 May 91 03:27:21 GMT
References: <02.May.91.132611.54@cogsci.cog.jhu.edu> <MEISSNER.91May3135345@curley.osf.org> <03.May.91.174910.55@cogsci.cog.jhu.edu>
Sender: news@mips.COM
Organization: MIPS Computer Systems, Inc.
Lines: 25
Nntp-Posting-Host: winchester.mips.com

In article <03.May.91.174910.55@cogsci.cog.jhu.edu> wjb@cogsci.cog.jhu.edu (Bill Bogstad) writes:
...
>	The idea behind this micro benchmark was to measure the overhead of
>a system call.  The getpid() and getppid() calls don't do any significant

AS usual, micro-level benchmarks can surprise you, and as architectural
variations arise, you can really get surprised.

As an example, register-window machines can be quite sensitive to
the depth of function calls, unlike most machines that are more sensitive
to the number of function calls.  For example, it is quite possible
for SPARC to look real good on getpid, but incur substantial overhead
on system calls that make many levels of calls into the kernel....

This is one more case where a micro-level benchmark gets zapped by
archiectural changes.  Besides the register-windows thing, one
can be surprised by:
	1) MMU subtleties
	2) Differences in cache design
	3) Differences in memory system design.
-- 
-john mashey	DISCLAIMER: <generic disclaimer, I speak for me only, etc>
UUCP: 	 mash@mips.com OR {ames,decwrl,prls,pyramid}!mips!mash 
DDD:  	408-524-7015, 524-8253 or (main number) 408-720-1700
USPS: 	MIPS Computer Systems MS 1/05, 930 E. Arques, Sunnyvale, CA 94088-3650