linux-kernel - Re: HalfSipHash Acceptable Usage

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Date:   Tue, 20 Dec 2016 21:29:24 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     George Spelvin <linux@...encehorizons.net>
Cc:     tytso@....edu, ak@...ux.intel.com, davem@...emloft.net,
        David.Laight@...lab.com, djb@...yp.to, ebiggers3@...il.com,
        hannes@...essinduktion.org, Jason@...c4.com,
        jeanphilippe.aumasson@...il.com,
        kernel-hardening@...ts.openwall.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, luto@...capital.net,
        netdev@...r.kernel.org, tom@...bertland.com,
        torvalds@...ux-foundation.org, vegard.nossum@...il.com
Subject: Re: HalfSipHash Acceptable Usage

On Tue, 2016-12-20 at 22:28 -0500, George Spelvin wrote:
> > I do not see why SipHash, if faster than MD5 and more secure, would be a
> > problem.
> 
> Because on 32-bit x86, it's slower.
> 
> Cycles per byte on 1024 bytes of data:
> 			Pentium	Core 2	Ivy
> 			4	Duo	Bridge
> SipHash-2-4		38.9	 8.3	 5.8
> HalfSipHash-2-4		12.7	 4.5	 3.2
> MD5			 8.3	 5.7	 4.7

So definitely not faster.

38 cycles per byte is a problem, considering IPV6 is ramping up.

But TCP session establishment on P4 is probably not a big deal.
Nobody would expect a P4 to handle gazillions of TCP flows (using a
32bit kernel)

What about SHA performance (syncookies) on P4 ?

Synfloods are probably the only case we might take care of for 2000-era
cpus.