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Re: VCE exceptions

To: "William J. Earl" <wje@fir.engr.sgi.com>
Subject: Re: VCE exceptions
From: ralf@uni-koblenz.de
Date: Fri, 3 Apr 1998 00:36:23 +0200
Cc: linux@cthulhu.engr.sgi.com
In-reply-to: <199804022141.NAA01565@fir.engr.sgi.com>; from William J. Earl on Thu, Apr 02, 1998 at 01:41:02PM -0800
References: <19980402225314.63238@uni-koblenz.de> <199804022141.NAA01565@fir.engr.sgi.com>
Sender: owner-linux@cthulhu.engr.sgi.com
On Thu, Apr 02, 1998 at 01:41:02PM -0800, William J. Earl wrote:

>  > Another way to finally eleminate the virtual coherency problem from
>  > KSEG0's landscape would be to actually use 8 pages as an array of
>  > empty_zero_pages[], so we would be able to map one wherever we want
>  > such that we never run into virtual coherency trouble.
> 
>       For an always-zero page, this is the best solution.  At a small
> cost in memory, you get far less overhead.

Indeed, 16ns on a 250Mhz machine for every exception that goes via the
general exception vector _plus_ the actual vce / vci handling, that sucks.
I just wonder why those exceptions have been implemented at all?

They may help somewhat in debugging operating systems, but in our situation
they're nervragging by their mere existance.

  Ralf

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