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From: ast@cs.vu.nl (Andy Tanenbaum)
Newsgroups: comp.os.minix
Subject: Re: Minix-ST context switch
Message-ID: <499@ast.cs.vu.nl>
Date: Wed, 16-Sep-87 10:38:42 EDT
Article-I.D.: ast.499
Posted: Wed Sep 16 10:38:42 1987
Date-Received: Sat, 19-Sep-87 01:41:48 EDT
References: <10647@orchid.waterloo.edu>
Reply-To: ast@cs.vu.nl (Andrew S. Tanenbaum)
Distribution: comp
Organization: VU Informatica, Amsterdam
Lines: 17

In article <10647@orchid.waterloo.edu> egisin@orchid.waterloo.edu (Eric Gisin) writes:
>I saw a message in comp.unix.wizards claiming the ST version
>of Minix implements context switching by copying the active process
>in and out of a fixed region of memory. Is this true?
>It would take about 100 millisecs to copy a 100k process in any out.
>

True enough, but the average MINIX process is about 5K, not 100K, so we
are talking 5 msec, not 100 msec.   Also, as soon as the child does an
exec, the funny business is finished and the exec'd core image runs
normally.  After the exec, the parent can be put back where it belongs
and both it and the child are not bothered with the relocation stuff any
more. In practice, the loss in performance is negligible.  This solution
was considered better than generating position independent code, which is
not very efficient.

Andy Tanenbaum (ast@cs.vu.nl)