From ea812ca1b06113597adcd8e70c0f84a413d97544 Mon Sep 17 00:00:00 2001 From: Alexander Duyck Date: Tue, 29 Jun 2010 18:38:00 +0000 Subject: [PATCH] x86: Align skb w/ start of cacheline on newer core 2/Xeon Arch x86 architectures can handle unaligned accesses in hardware, and it has been shown that unaligned DMA accesses can be expensive on Nehalem architectures. As such we should overwrite NET_IP_ALIGN to resolve this issue. Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Signed-off-by: Alexander Duyck Signed-off-by: Jeff Kirsher Acked-by: H. Peter Anvin Signed-off-by: David S. Miller --- arch/x86/include/asm/system.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h index b8fe48e..b4293fc 100644 --- a/arch/x86/include/asm/system.h +++ b/arch/x86/include/asm/system.h @@ -457,4 +457,13 @@ static inline void rdtsc_barrier(void) alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC); } +#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 */ -- 2.7.4