From 3af722cb735d212554027ec81e2aa2e6bf1ee34d Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Tue, 8 Mar 2022 17:12:10 +0100 Subject: powerpc/net: Implement powerpc specific csum_shift() to remove branch Today's implementation of csum_shift() leads to branching based on parity of 'offset' 000002f8 : 2f8: 70 a5 00 01 andi. r5,r5,1 2fc: 41 a2 00 08 beq 304 300: 54 84 c0 3e rotlwi r4,r4,24 304: 7c 63 20 14 addc r3,r3,r4 308: 7c 63 01 94 addze r3,r3 30c: 4e 80 00 20 blr Use first bit of 'offset' directly as input of the rotation instead of branching. 000002f8 : 2f8: 54 a5 1f 38 rlwinm r5,r5,3,28,28 2fc: 20 a5 00 20 subfic r5,r5,32 300: 5c 84 28 3e rotlw r4,r4,r5 304: 7c 63 20 14 addc r3,r3,r4 308: 7c 63 01 94 addze r3,r3 30c: 4e 80 00 20 blr And change to left shift instead of right shift to skip one more instruction. This has no impact on the final sum. 000002f8 : 2f8: 54 a5 1f 38 rlwinm r5,r5,3,28,28 2fc: 5c 84 28 3e rotlw r4,r4,r5 300: 7c 63 20 14 addc r3,r3,r4 304: 7c 63 01 94 addze r3,r3 308: 4e 80 00 20 blr Seems like only powerpc benefits from a branchless implementation. Other main architectures like ARM or X86 get better code with the generic implementation and its branch. Signed-off-by: Christophe Leroy Signed-off-by: David S. Miller --- arch/powerpc/include/asm/checksum.h | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'arch/powerpc/include/asm/checksum.h') diff --git a/arch/powerpc/include/asm/checksum.h b/arch/powerpc/include/asm/checksum.h index 350de8f90250..ab3832b93f0a 100644 --- a/arch/powerpc/include/asm/checksum.h +++ b/arch/powerpc/include/asm/checksum.h @@ -112,6 +112,13 @@ static __always_inline __wsum csum_add(__wsum csum, __wsum addend) #endif } +#define HAVE_ARCH_CSUM_SHIFT +static __always_inline __wsum csum_shift(__wsum sum, int offset) +{ + /* rotate sum to align it with a 16b boundary */ + return (__force __wsum)rol32((__force u32)sum, (offset & 1) << 3); +} + /* * This is a version of ip_compute_csum() optimized for IP headers, * which always checksum on 4 octet boundaries. ihl is the number -- cgit v1.2.3-59-g8ed1b