Messages in this thread | | | Date | Wed, 8 Feb 2023 21:48:08 +0800 | Subject | Re: [PATCH] LoongArch: add checksum optimization for 64-bit system | From | WANG Xuerui <> |
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On 2023/2/8 21:12, David Laight wrote: > From: Bibo Mao >> Sent: 07 February 2023 04:02 >> >> loongArch platform is 64-bit system, which supports 8 bytes memory >> accessing, generic checksum function uses 4 byte memory access. >> This patch adds 8-bytes memory access optimization for checksum >> function on loongArch. And the code comes from arm64 system. >> >> When network hw checksum is disabled, iperf performance improves >> about 10% with this patch. >> > ... >> +static inline __sum16 csum_fold(__wsum csum) >> +{ >> + u32 sum = (__force u32)csum; >> + >> + sum += (sum >> 16) | (sum << 16); >> + return ~(__force __sum16)(sum >> 16); >> +} > > Does LoongArch have a rotate instruction? > But for everything except arm (which has a rotate+add instruction) > the best is (probably): > (~sum - rol32(sum, 16)) >> 16 > > To the point where it is worth killing all the asm > versions and just using that one.
Yeah LoongArch can do rotates, and your suggestion can indeed reduce one insn from every invocation of csum_fold.
From this:
000000000000096c <csum_fold>: sum += (sum >> 16) | (sum << 16); 96c: 004cc08c rotri.w $t0, $a0, 0x10 970: 00101184 add.w $a0, $t0, $a0 return ~(__force __sum16)(sum >> 16); 974: 0044c084 srli.w $a0, $a0, 0x10 978: 00141004 nor $a0, $zero, $a0 } 97c: 006f8084 bstrpick.w $a0, $a0, 0xf, 0x0 980: 4c000020 jirl $zero, $ra, 0
To:
0000000000000984 <csum_fold2>: return (~sum - rol32(sum, 16)) >> 16; 984: 0014100c nor $t0, $zero, $a0 return (x << amt) | (x >> (32 - amt)); 988: 004cc084 rotri.w $a0, $a0, 0x10 return (~sum - rol32(sum, 16)) >> 16; 98c: 00111184 sub.w $a0, $t0, $a0 } 990: 00df4084 bstrpick.d $a0, $a0, 0x1f, 0x10 994: 4c000020 jirl $zero, $ra, 0
I guess Bibo would take this suggestion and check the other arches afterwards, okay? ;-)
-- WANG "xen0n" Xuerui
Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/
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