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

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Date:   Wed, 6 Sep 2023 14:38:49 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Noah Goldstein' <goldstein.w.n@...il.com>,
        "x86@...nel.org" <x86@...nel.org>
CC:     "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

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.

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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