From: Alexander Duyck <alexander.h.duyck@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 to resolve
this issue.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
---
arch/x86/include/asm/system.h | 9 +++++++++
1 files changed, 9 insertions(+), 0 deletions(-)
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 */
--
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