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From: terry@cs.weber.edu (Terry Lambert)
Message-Id: <9506081814.AA03515@cs.weber.edu>
Subject: Re: 2.0.5-A: Very disheartening?
To: phk@ref.tfs.com (Poul-Henning Kamp)
Date: Thu, 8 Jun 95 12:14:20 MDT
Cc: uhclem%nemesis@fw.ast.com, jgreco@brasil.moneng.mei.com,
        hackers@freebsd.org, bugs@freebsd.org
In-Reply-To: <199506080331.UAA05773@ref.tfs.com> from "Poul-Henning Kamp" at Jun 7, 95 08:31:14 pm
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> > Try it to humor me?  Have anything else to try that you are more confident
> 
> Terry, you may be unfamiliar with x86 terminology.  All I tried to say
> was that the transfer to the uncompressed code was a "far jump" which 
> until now has always flushed the prefetch.  You only need to bother
> with the prefetch queue if you modify instructions in you close
> neighborhood.

According to a posting a while back in the linux developer news group,
there was an issue with jumps *not* flushing the prefetch queue that
was throwing off a CPU timing test of some kind.  I forget the details.

It was not clear that the "far jump" in fact covered "a large distance"
or was simply being used as a prefetch flushing mechanism.  What I was
suggesting was an alternate flushing mechanism (filling the thing up
with NOPs).

I guess a question I have is how the distinction is made between I and D
in the code leading up to the kernel being executed.


					Terry Lambert
					terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.