linux-kernel - Re: x86/csum: Remove unnecessary odd handling

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Message-ID: <CAFUsyfLPLQBs2gQwLDUZHudQrkHSXCcV=Wi0=Znb3gChDZvX2Q@mail.gmail.com>
Date:   Wed, 20 Sep 2023 14:20:24 -0500
From:   Noah Goldstein <goldstein.w.n@...il.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>
Subject: Re: x86/csum: Remove unnecessary odd handling

On Wed, Sep 6, 2023 at 9:38 AM David Laight <David.Laight@...lab.com> wrote:
>
> From: Noah Goldstein
> > Sent: 01 September 2023 23:21
> ...
> > +     return add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
>
> The generic C alternative:
>         return (temp64 + ror64(temp64, 32)) >> 32;
> is the same number of instructions but might get
> better scheduling.
>
Sorry, I missed this.
Bright idea :)
Adding in new version + you reviewed by tag. Then hopefully this can
get in...

> The C version of csum_fold() from arc/include/asm/checksum.h
> is also better than the x86 asm version.
> (And also pretty much all the other architecture dependant
> copies.)
>
>         David
>
> -
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