From 614b4f5d0fa3f622cfcc899491d8a3e6af3d4dc5 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Tue, 11 Aug 2020 16:36:26 +0200 Subject: [PATCH] s390/checksum: make ip_fast_csum() faster Convert ip_fast_csum() so it doesn't call csum_partial(), but instead open code the checksum calculation. The problem with csum_partial() is that it makes use of the cksm instruction, which has high startup costs and therefore is only very fast if used on larger memory regions. IPv4 headers however are small in size (5-16 32-bit words). The open coded variant calculates the checksum in ~30% of the time compared to the old variant (z14, march=z196). Signed-off-by: Heiko Carstens Signed-off-by: Vasily Gorbik --- arch/s390/include/asm/checksum.h | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/s390/include/asm/checksum.h b/arch/s390/include/asm/checksum.h index 961c25c..8bc6bed 100644 --- a/arch/s390/include/asm/checksum.h +++ b/arch/s390/include/asm/checksum.h @@ -66,7 +66,18 @@ static inline __sum16 csum_fold(__wsum sum) */ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl) { - return csum_fold(csum_partial(iph, ihl*4, 0)); + __u64 csum = 0; + __u32 *ptr = (u32 *)iph; + + csum += *ptr++; + csum += *ptr++; + csum += *ptr++; + csum += *ptr++; + ihl -= 4; + while (ihl--) + csum += *ptr++; + csum += (csum >> 32) | (csum << 32); + return csum_fold((__force __wsum)(csum >> 32)); } /* -- 2.7.4