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From: Jeff Kirsher on 2 Jun 2010 18:30
From: Alexander Duyck <alexander.h.duyck(a)intel.com>

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 and NET_SKB_PAD
to resolve this issue.

Signed-off-by: Alexander Duyck <alexander.h.duyck(a)intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher(a)intel.com>
---

arch/x86/include/asm/system.h | 12 ++++++++++++
1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h
index b8fe48e..8acb44e 100644
--- a/arch/x86/include/asm/system.h
+++ b/arch/x86/include/asm/system.h
@@ -457,4 +457,16 @@ 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.
+ * We also modify NET_SKB_PAD to be a cacheline in size, thus maintaining
+ * cacheline alignment of buffers.
+ */
+#define NET_IP_ALIGN 0
+#define NET_SKB_PAD L1_CACHE_BYTES
+#endif
#endif /* _ASM_X86_SYSTEM_H */

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