*BSD News Article 39650


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From: wes@indirect.com (Barnacle Wes)
Subject: Re: How fast? [was: ... slugish ...]
Message-ID: <D0ytA9.K0K@indirect.com>
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Organization: the Briney (notso) Deep
Date: Sat, 17 Dec 1994 17:15:45 GMT
References: <1994Nov28.194617.18912@system9.unisys.com> <3bf6ou$pm7@wup-gate.wup.de> <MICHAELV.94Dec9223853@MindBender.HeadCandy.com> <3cs7rd$k1u@news.demos.su>
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Ivan Popov (pin@demos.su) wrote:
: I tried to compile same package (screen control libraries)
: on the same computer (386/25, 4Mb RAM)
: under FreeBSD-2.0 (generic kernel)
: and under Demos-86 (real mode UNIX for i8086 [sic], using 640K mem
:                     with /tmp in extended memory).

: The result: _user_ times used are almost the same (about 17 min)
:             _real_ times used are: 50 min under Demos-86,
:                                    90 min under FreeBSD-2.0
: The difference between user and real times was due to I/O and swapping.
: (BTW in the case of Demos-86 all passes of the compiler and make itself
: fit into 640K, hence almost no swapping)

Oh, there are a lot of other differences, too.  Your real-mode UNIX
probably uses a software interrupt for kernel calls, whereas the
protected-mode FreeBSD has to use call gates to cross protection
rings, and has to do some page-table frobbing, etc.  The overhead
of a virtual memory system isn't so much surprising as disappointing.

	Wes Peters