Message-ID: <3F65C611.80203@cyberone.com.au>
Date: Tue, 16 Sep 2003 00:00:49 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: Chris Meadors <twrchris@hereintown.net>
CC: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata
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Chris Meadors wrote:

>On Mon, 2003-09-15 at 08:38, Nick Piggin wrote:
>
>
>>OK, the reason why I don't like the sound of this is because the size
>>of your option set has now been squared, and its no longer "make these
>>CPUs work".
>>
>
>The way I see the config option working is, having a sub-menu that says
>something like, "Select the CPU the kernel will be run on."  From there
>you can pick one CPU.  This sets the in kernel optimizations for that
>CPU, along with the work arounds (obviously).  It also sets the compiler
>flags for the padding, and "-march=[CPU]".  Then in a sub-menu of this
>menu, there is an "Advanced processor selection".  The help text would
>be something like, "In addition to the primary processor selected above,
>also allow this kernel to be booted on the processors selected below. 
>Selecting this option disables some of the optimizations for the primary
>processor."  Just turning on that option would change the "-march=" to
>"-mcpu=".  Then in the menu one could select from any of the CPUs
>listed.  Each one would enable the work around code to allow the built
>kernel to run correctly on a machine with a different CPU.
>
>I see this as sort of like the advanced partition selection, or the
>compiled in fonts.
>

Look at the complexity though!

>
>>I can see an argument for cache line size but thats about it. I can't
>>think of my optimisations that should be done on one architecture but
>>not another.
>>
>
>Don't forget the compiler optimization flags.  A kernel built with
>"-march" may not run on any other CPUs.
>

Yeah, I really meant _should_, not must. In other words, something that
is an optimisation for one architecutre, but a pessimisation for
another.

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