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Re: [RFC] Optimize swab operations on mips_r2 cpu

To: "Franck" <vagabon.xyz@gmail.com>, "Nigel Stephens" <nigel@mips.com>
Subject: Re: [RFC] Optimize swab operations on mips_r2 cpu
From: "Kevin D. Kissell" <kevink@mips.com>
Date: Fri, 27 Jan 2006 11:13:44 +0100
Cc: <linux-mips@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
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> > You could, but why not stick with -march=4ksd if that's your CPU of
> > choice? It appears to result in  marginally smaller code even when using
> > -Os, and should have (slightly) better performance than a generic
> > mips32r2 kernel?
> 
> Just to avoid a new CPU_4KSD definition in the kernel code as
> suggested by Kevin. Basically all mips32r2 specific code is the same
> as 4ksd specific code (except the code that deals with SmartMIPS
> extension). So it can use CONFIG_CPU_MIPS32_R2 macro. But I was not
> aware of -march=4ksd and -march=mips32r2 differences. Maybe now it is
> needed to have a new CPU_4KSD definition ?

Configuration hacks that are specific to a single core create cruft and
maintenence problems.  As I said yesterday, I think we'd be much better
off to have a CONFIG_CPU_MIPS_SMALL or some such option
that could cause -Os to be used, allow branch-likelies, etc. The optimizations
under discussion aren't at all specific to the 4KSd, and I would think that
for every 4KSd embedded Linux platform there are several 4KEc platforms
that would benefit from a smaller kernel footprint.

It's Linux, and people can do what they want, but I'd prefer not to see more
core-specifc cruft work its way back into the linux-mips or kernel.org reference
trees.

            Regards,

            Kevin K.

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