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authorChristophe Leroy <christophe.leroy@csgroup.eu>2022-03-08 19:12:10 +0300
committerDavid S. Miller <davem@davemloft.net>2022-03-11 13:57:22 +0300
commit3af722cb735d212554027ec81e2aa2e6bf1ee34d (patch)
treee1f7caba28268fb626893bc719540414f3272248 /include/net/checksum.h
parent8ef1dc4d204a5329eeeaf6edd9b62f6f2a64ebef (diff)
downloadlinux-3af722cb735d212554027ec81e2aa2e6bf1ee34d.tar.xz
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 <csum_block_add>: 2f8: 70 a5 00 01 andi. r5,r5,1 2fc: 41 a2 00 08 beq 304 <csum_block_add+0xc> 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 <csum_block_add>: 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 <csum_block_add>: 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 <christophe.leroy@csgroup.eu> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/checksum.h')
-rw-r--r--include/net/checksum.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/net/checksum.h b/include/net/checksum.h
index 79c67f14c448..6bc783b7a06c 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -80,6 +80,7 @@ static __always_inline __sum16 csum16_sub(__sum16 csum, __be16 addend)
return csum16_add(csum, ~addend);
}
+#ifndef HAVE_ARCH_CSUM_SHIFT
static __always_inline __wsum csum_shift(__wsum sum, int offset)
{
/* rotate sum to align it with a 16b boundary */
@@ -87,6 +88,7 @@ static __always_inline __wsum csum_shift(__wsum sum, int offset)
return (__force __wsum)ror32((__force u32)sum, 8);
return sum;
}
+#endif
static __always_inline __wsum
csum_block_add(__wsum csum, __wsum csum2, int offset)