netdev - Re: [PATCH v2] gianfar: Fall back to software tcp/udp checksum on oldercontrollers

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Message-ID: <20110128105610.4a518456@udp111988uds.am.freescale.net>
Date:	Fri, 28 Jan 2011 10:56:10 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	<netdev@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2] gianfar: Fall back to software tcp/udp checksum on
 oldercontrollers

On Fri, 28 Jan 2011 09:10:46 +0000
David Laight <David.Laight@...LAB.COM> wrote:

>  
> > +		if (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12)
> > +			     && ((unsigned long)fcb % 0x20) > 0x18)) {
> 
> You need to check the generated code, but I think you need:
> 
>     if (unlikely(gfar_has_errata(priv, GFAR_ERRATA_12))
> 	     && unlikely(((unsigned long)fcb % 0x20) > 0x18))
> 
> ie unlikely() around both the primitive comparisons.

Is the first condition actually unlikely?  If you've got affected
hardware, you'll hit it every time.

If packets with the problematic alignment are rare, seems like it'd be
better to check that first.

-Scott

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