netdev - RE: [PATCH] mlx4_en: fix transmit of packages when blue frame isenabled

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Date:	Sun, 09 Oct 2011 09:28:51 +0200
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Eli Cohen <eli@....mellanox.co.il>,
	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>,
	Eli Cohen <eli@...lanox.co.il>,
	Yevgeny Petrilin <yevgenyp@...lanox.co.il>,
	linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org
Subject: RE: [PATCH] mlx4_en: fix transmit of packages when blue frame
 isenabled

On Thu, 2011-10-06 at 15:10 +0100, David Laight wrote:
> horrid...
> 1) I'm not sure the caller expects the buffer to be corrupted.
> 2) It contains a lot of memory cycles.
> 3) It looked from the calls that this code is copying descriptors,
>    so the transfer length is probably 1 or 2 words - so the loop
>    is inefficient.
> 4) ppc doesn't have a fast byteswap instruction (very new gcc might
>    use the byteswapping memery access for the le32_to_cpu() though),
>    so it would be better getting the byteswap done inside
>    __iowrite64_copy() - since that is probably requesting a byteswap
>    anyway.
> OTOH I'm not at all clear about the 64bit xfers....

And it's just plain wrong anyway. You should never have to byteswap a
copy.

Ben.


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