Subject: [RFC] skb align patch

From: Stephen Hemminger <[email-masked]>
Date: Sun, 20 Sep 2009 14:22:12 -0700

Based on the Intel suggestion that PCI-express overhead is
a significant cost.

Would people doing performance please measure the impact of
changing SKB alignment (64 bit only).

--- a/arch/x86/include/asm/system.h	2009-09-20 14:08:40.922346912 -0700
+++ b/arch/x86/include/asm/system.h	2009-09-20 14:14:37.012371200 -0700
@@ -455,4 +455,14 @@ static inline void rdtsc_barrier(void)
 	alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
 }
 
+#ifndef CONFIG_X86_32
+/*
+ * DMA to unaligned address is more expensive than the the
+ * overhead of unaligned CPU access.
+ */
+#define NET_IP_ALIGN	0
+#define NET_SKB_PAD	L1_CACHE_BYTES
+#endif
+
+
 #endif /* _ASM_X86_SYSTEM_H */