netdev - Re: [PATCH net-next 1/6] net: Allow csum

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Date:	Fri, 04 Apr 2014 18:34:51 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 1/6] net: Allow csum_add to be provided in arch

On Fri, 2014-04-04 at 17:26 -0700, Tom Herbert wrote:
> csum_add is really nothing more then add-with-carry which
> can be implemented efficiently in some architectures.
> Allow architecture to define this protected by HAVE_ARCH_CSUM_ADD.
> 
> Provide csum_add in for x86.

[ net-next is closed during merge window ]

Not x86, but x86_64 only.

Note add32_with_carry(a, b) is suboptimal, as it forces
a and b in registers.

b could be a memory or a register operand.

diff --git a/arch/x86/include/asm/checksum_64.h b/arch/x86/include/asm/checksum_64.h
index e6fd8a026c7b..29f130d3c344 100644
--- a/arch/x86/include/asm/checksum_64.h
+++ b/arch/x86/include/asm/checksum_64.h
@@ -184,7 +184,7 @@ static inline unsigned add32_with_carry(unsigned a, unsigned b)
        asm("addl %2,%0\n\t"
            "adcl $0,%0"
            : "=r" (a)
-           : "0" (a), "r" (b));
+           : "0" (a), "rm" (b));
        return a;
 }




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