kern/178467: [zfs] [request] Optimized Checksum Code for ZFS

[Alan Somers]

The following reply was made to PR kern/178467; it has been noted by GNATS.

From: Alan Somers <asomers at freebsd.org>
To: bug-followup at FreeBSD.org, jkeller at bbiinternational.com
Cc:  
Subject: Re: kern/178467: [zfs] [request] Optimized Checksum Code for ZFS
Date: Mon, 24 Jun 2013 09:28:08 -0600

 FWIW, I spent a full day trying to accelerate Fletcher-4 using SIMD
 instructions (tested on Sandy Bridge and Nehalem).  I was unable to
 improve on the current code; the Fletcher-4 hash is very fast and
 doesn't vectorize well.  However, I believe that AVX-2 will probably
 be able to beat the non-vectorized version.  I plan to try it out as
 soon as I can get my hands on a Haswell CPU.  I've also spent several
 weeks analyzing the strength of Fletcher-4, and concluded that it's
 really quite good.  Good enough for every non-cryptographic
 application, certainly.  My recommendation is that all ZFS users
 should prefer Fletcher-4 over SHA-256.  I haven't tried vectorizing
 SHA-256 and don't plan to.