Newsgroups: comp.os.minix
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Why the 8086 architecture is wonderful :-)
Message-ID: <1989Mar22.194041.3321@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1989Mar16.184945.23152@utzoo.uucp> <88236@felix.UUCP>
Date: Wed, 22 Mar 89 19:40:41 GMT

In article <88236@felix.UUCP> preston@felix.UUCP (Preston Bannister) writes:
>Er, Henry are you saying that fork() without an MMU is NOT hundreds
>or thousands of times as expensive as with an MMU? :-) :-)

If the programs are small, yes, that's exactly what I'm saying.  Maybe
two or three times more expensive, but NOT hundreds or thousands.

>If you are forking the shell to exec() a program in response to user
>typed command making a copy of the shell's address space as part of
>the fork() is no big deal.  Forking GNU Emacs (or some other large
>program) to exec() _is_ likely to be painful.  

Well, serves you right for running such elephantine software! :-)
The GNU software is quite explicitly built for tomorrow's machines,
or maybe the next millenium but one's, not today's.

>The previous poster's example of communications program that uses
>fork() to generate a clone of itself is _enormously_ inefficent if
>the child and parent have to be swapped around in memory of each
>process switch.

Yes, that particular case -- where an exec() is not imminent, which
it *is* in almost all forks -- needs special handling on such systems.


Note that I didn't say it was wonderful in general; I said it was not
a big problem under Minix (which tends to avoid elephantine programs).
-- 
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