linux-kernel - RE: [PATCH] LoongArch: add checksum optimization for 64-bit system

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <7636a7bebfd44e378c5b16d6fd355232@AcuMS.aculab.com>
Date:   Wed, 8 Feb 2023 14:19:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'WANG Xuerui' <kernel@...0n.name>,
        'Bibo Mao' <maobibo@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
CC:     Jiaxun Yang <jiaxun.yang@...goat.com>,
        "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] LoongArch: add checksum optimization for 64-bit system

From: WANG Xuerui
> Sent: 08 February 2023 13:48
...
> 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

It is actually slightly better than that.
In the csum_fold2 version the first two instructions
are independent - so can execute in parallel on some cpu.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)