linux-kernel - RE: [PATCH 04/18] csum_and_copy_..._user(): pass 0xffffffff instead of 0 as initial sum

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Message-ID: <1ba695b2264349f187f825ff2c308624@AcuMS.aculab.com>
Date:   Thu, 23 Jul 2020 15:36:52 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Al Viro' <viro@...iv.linux.org.uk>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: RE: [PATCH 04/18] csum_and_copy_..._user(): pass 0xffffffff instead
 of 0 as initial sum

From: Al Viro
> Sent: 23 July 2020 16:21
...
> The point is, your "~4.5 cycles per vector" is pretty much noise and the
> difference between the 3-argument and 4-argument variants could easily be
> in the same range.  It might be a valid microoptimization, it might be not.
> 3-argument variant is simpler and IMO in absence of strong data we ought
> to go with that.

There is definitely more to be gained by rewriting the x86-86 asm.

	David

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