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From: Guido van Rooij <guido@gvr.win.tue.nl>
Message-Id: <199704110739.JAA06258@gvr.win.tue.nl>
Subject: Re: cvs commit:  src/sys/i386/i386 genassym.c machdep.c trap.c src/sys/i386/include pcb.h
In-Reply-To: <199704101705.DAA13021@godzilla.zeta.org.au> from Bruce Evans at "Apr 11, 97 03:05:12 am"
To: bde@zeta.org.au (Bruce Evans)
Date: Fri, 11 Apr 1997 09:39:18 +0200 (MET DST)
Cc: peter@freefall.freebsd.org, cvs-all@freefall.freebsd.org,
        CVS-committers@freefall.freebsd.org, cvs-sys@freefall.freebsd.org
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Bruce Evans wrote:
> >>   This change makes VM86 mode harder, but the following commits will remove
> >>   a lot of constraints for the VM86 system, including the possibility of
> >>   extending the pcb for an IO port map etc.
> >
> >Yes! Finally get rid of the old /dev/io hack ;-)
> 
> It would mainly make things more complicated and cost more.  Accesses
> through the port map cost 20 cycles extra.  There would be up to 64K of
> ports to manage.  Who knows where the DMA ports (if any) on new video
> cards are?

The extra cost is only for ppl using the io port map. As far as I understand
it this map is optional. When non-present you don't have to fiddle
with it. So the performance penalty is only for those ppl.

-Guido