Subject: Re: [net-next-2.6 PATCH v2] x86: Align skb w/ start of cacheline on newer core 2/Xeon Arch

From: Alexander Duyck <[email-masked]>
Date: Thu, 01 Jul 2010 13:37:27 -0700

Andi Kleen wrote:
> Jeff Kirsher <[email-masked]> writes:
> 
> 
> Sorry for the late comment.
> 
>>  
>> +#ifdef CONFIG_MCORE2
>> +/*
>> + * We handle most unaligned accesses in hardware.  On the other hand
>> + * unaligned DMA can be quite expensive on some Nehalem processors.
>> + *
>> + * Based on this we disable the IP header alignment in network drivers.
>> + */
>> +#define NET_IP_ALIGN	0
>> +#endif
>>  #endif /* _ASM_X86_SYSTEM_H */
> 
> The ifdef should be imho dropped and the option be made unconditional
> for all x86. I am not aware of any x86 core where unalignment is really
> slow. This would increase the chance of it actually working on many
> configurations which do not necessarily optimize for Core2.
> 
> -Andi

Seems to make sense to me.  I will see about generating a patch that 
drops the check for CONFIG_MCORE2.

Thanks,

Alex