linux-kernel - Re: [RFC PATCH 3/3] x86/lib: Use EGPRs in 64-bit checksum copy loop

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Message-ID: <0fef00d6-b7f9-47aa-8f4d-1b4c6c4ebb3f@intel.com>
Date: Mon, 1 Dec 2025 13:39:31 -0800
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: david laight <david.laight@...box.com>
CC: <linux-kernel@...r.kernel.org>, <x86@...nel.org>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>
Subject: Re: [RFC PATCH 3/3] x86/lib: Use EGPRs in 64-bit checksum copy loop

On 11/25/2025 2:37 AM, david laight wrote:
> 
> This code (or something very similar) gets used to checksum data
> during copy_to/from_user for sockets.
> This goes back a long way and I suspect the 'killer ap' was nfsd
> running over UDP (with 8k+ UDP datagrams).
> Modern NICs all (well all anyone cares about) to IP checksum offload.
> So you don't need to checksum on send() - I'm sure that is still
> enabled even though you pretty much never want it.
> The checksum on recv() can only happen for UDP, but massively
> complicates the code paths and will normally not be needed.

It sounds like this optimization wouldn't provide practical benefit. I 
don't see a strong case for pursuing this further either, so I'd drop this.

Thanks,
Chang