arm64: mm: define NET_IP_ALIGN to 0
authorArd Biesheuvel <ard.biesheuvel@linaro.org>
Wed, 7 Nov 2018 17:10:38 +0000 (18:10 +0100)
committerCatalin Marinas <catalin.marinas@arm.com>
Thu, 8 Nov 2018 17:50:26 +0000 (17:50 +0000)
On arm64, there is no need to add 2 bytes of padding to the start of
each network buffer just to make the IP header appear 32-bit aligned.

Since this might actually adversely affect DMA performance some
platforms, let's override NET_IP_ALIGN to 0 to get rid of this
padding.

Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
arch/arm64/include/asm/processor.h

index 3e20917..6b0d4df 100644 (file)
 #define KERNEL_DS      UL(-1)
 #define USER_DS                (TASK_SIZE_64 - 1)
 
+/*
+ * On arm64 systems, unaligned accesses by the CPU are cheap, and so there is
+ * no point in shifting all network buffers by 2 bytes just to make some IP
+ * header fields appear aligned in memory, potentially sacrificing some DMA
+ * performance on some platforms.
+ */
+#define NET_IP_ALIGN   0
+
 #ifndef __ASSEMBLY__
 #ifdef __KERNEL__