linux-kernel - Re: [PATCH v2 2/2] powerpc32: optimise csum

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Message-ID: <20150806003059.GD18479@gate.crashing.org>
Date:	Wed, 5 Aug 2015 19:30:59 -0500
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Christophe Leroy <christophe.leroy@....fr>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>, scottwood@...escale.com,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] powerpc32: optimise csum_partial() loop

On Wed, Aug 05, 2015 at 03:29:35PM +0200, Christophe Leroy wrote:
> On the 8xx, load latency is 2 cycles and taking branches also takes
> 2 cycles. So let's unroll the loop.

This is not true for most other 32-bit PowerPC; this patch makes
performance worse on e.g. 6xx/7xx/7xxx.  Let's not!


Segher
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