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Re: [PATCH] mm/pg-r4k.c: Dump the generated code

To: "Maciej W. Rozycki" <macro@linux-mips.org>
Subject: Re: [PATCH] mm/pg-r4k.c: Dump the generated code
From: Franck Bui-Huu <vagabon.xyz@gmail.com>
Date: Sun, 14 Oct 2007 21:32:44 +0200
Cc: Ralf Baechle <ralf@linux-mips.org>, Thiemo Seufer <ths@networkno.de>, linux-mips@linux-mips.org
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Maciej W. Rozycki wrote:
> On Tue, 9 Oct 2007, Franck Bui-Huu wrote:
> 
>>>  What would be the gain for the kernel from using "-march=4ksd" rather 
>>> than "-march=mips32r2"?
>>>
>> It actually results in a kernel image ~30kbytes smaller for the former
>> case. It has been discussed sometimes ago on this list. I'm sorry but
>> I don't know why...
> 
>  Perhaps the pipeline description for the 4KSd CPU is different from the 
> default for the MIPS32r2 ISA.  Barring a study of GCC sources, if that 
> really troubles you, you could build the same version of the kernel with 
> these options:
> 
> 1. "-march=mips32r2"
> 
> 2. "-march=4ksd"
> 
> 3. "-march=mips32r2 -mtune=4ksd"
> 
> and compare the results.  I expect the results of #2 and #3 to be the same 
> and it would just back up my suggestion about keeping CPU-specific 
> optimisations separate from the CPU selection.

I think you misunderstood me, my own fault: the kernel was smaller
with "-march=4ksd". It was bigger when using "-march=mips32r2 -smartmips".

I was using SDE gcc.

                Franck


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