netdev - Re: [PATCH] ipv4: IP defragmentation must be ECN aware

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Date:	Wed, 5 Jan 2011 09:48:30 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ipv4: IP defragmentation must be ECN aware

On Wed, 05 Jan 2011 18:41:01 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le mercredi 05 janvier 2011 à 09:13 -0800, Stephen Hemminger a écrit :
> > On Wed, 05 Jan 2011 14:59:02 +0100
> > Eric Dumazet <eric.dumazet@...il.com> wrote:
> > 
> > > +
> > > +static inline int ip4_frag_ecn(int tos)
> > 
> > Since tos is only a byte, this should be:
> > 
> > static inline u8 ip4_frag_ecn(u8 tos)
> > 
> > 
> 
> In fact, generated code is the same on x86, but some arches have faster
> arithmetic on WORD units.
> 
> And I added the 'inline' because on x86_64 gcc, compiler chose _not_ to
> inline this 6 instruction sequence ! Code was much larger.
> 
> 31 d2                   xor    %edx,%edx
> 0f b6 40 01             movzbl 0x1(%rax),%eax
> 83 e0 03                and    $0x3,%eax
> ff c0                   inc    %eax
> a8 02                   test   $0x2,%al
> 0f 44 d0                cmove  %eax,%edx
> 
> 
> We do roughly the same (working on WORD arith) in 
>
At least make it unsigned int?

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