linux-kernel - Re: [PATCH] lib/crc32: slice by 4 is more efficient than the default slice by 8 on Powerpc 8xx.

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Message-ID: <1384904608.1403.395.camel@snotra.buserror.net>
Date:	Tue, 19 Nov 2013 17:43:28 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
CC:	Christophe Leroy <christophe.leroy@....fr>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	Marcelo Tosatti <marcelo@...ck.org>,
	Bob Pearson <rpearson@...temfabricworks.com>
Subject: Re: [PATCH] lib/crc32: slice by 4 is more efficient than the
 default slice by 8 on Powerpc 8xx.

On Wed, 2013-11-20 at 00:39 +0100, Joakim Tjernlund wrote:
> Scott Wood <scottwood@...escale.com> wrote on 2013/11/19 19:29:26:
> > 
> > I don't think we should go littering the Kconfig with defaults for
> > various bits of hardware -- especially since you've already pointed out
> > non-8xx hardware that would also want this.  Put it in defconfig
> > instead, unless you can identify very broad classes of machines for
> > which SLICEBY4 is faster.
> 
> hmm, when 64bits went in there was not much proof that it was faster for
> a wide range of CPU, just 2 or 3 if I recall correctly. I suspect there
> are quite a few CPUs where 32 bits a equal or faster.

That may be the case, but I don't think we want a big list of them in
lib/Kconfig.  Whether the default should change (for all targets that
don't override it in defconfig, or at least for some broader category
such as "all 32-bit chips") is a different discussion.

-Scott



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