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

From: Andi Kleen <[email-masked]>
Date: Thu, 01 Jul 2010 13:28:13 +0200

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
-- 
[email-masked] -- Speaking for myself only.