From 1e7196fa5b0312a6a3e49e7c1300e145afcba96b Mon Sep 17 00:00:00 2001 From: Charlie Jenkins Date: Mon, 8 Jan 2024 15:57:02 -0800 Subject: [PATCH] asm-generic: Improve csum_fold This csum_fold implementation introduced into arch/arc by Vineet Gupta is better than the default implementation on at least arc, x86, and riscv. Using GCC trunk and compiling non-inlined version, this implementation has 41.6667%, 25% fewer instructions on riscv64, x86-64 respectively with -O3 optimization. Most implmentations override this default in asm, but this should be more performant than all of those other implementations except for arm which has barrel shifting and sparc32 which has a carry flag. Signed-off-by: Charlie Jenkins Reviewed-by: David Laight Link: https://lore.kernel.org/r/20240108-optimize_checksum-v15-1-1c50de5f2167@rivosinc.com Signed-off-by: Palmer Dabbelt --- include/asm-generic/checksum.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/include/asm-generic/checksum.h b/include/asm-generic/checksum.h index 43e18db89c14..ad928cce268b 100644 --- a/include/asm-generic/checksum.h +++ b/include/asm-generic/checksum.h @@ -2,6 +2,8 @@ #ifndef __ASM_GENERIC_CHECKSUM_H #define __ASM_GENERIC_CHECKSUM_H +#include + /* * computes the checksum of a memory block at buff, length len, * and adds in "sum" (32-bit) @@ -31,9 +33,7 @@ extern __sum16 ip_fast_csum(const void *iph, unsigned int ihl); static inline __sum16 csum_fold(__wsum csum) { u32 sum = (__force u32)csum; - sum = (sum & 0xffff) + (sum >> 16); - sum = (sum & 0xffff) + (sum >> 16); - return (__force __sum16)~sum; + return (__force __sum16)((~sum - ror32(sum, 16)) >> 16); } #endif