Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920

[Maho NAKATA]

From: Michael Poole <mdpoole at troilus.org>
Subject: Re: Only 70% of theoretical peak performance on FreeBSD 8/amd64, Corei7 920
Date: Mon, 12 Apr 2010 10:06:55 -0400

> Nakata-san's theoretical performance numbers assume 4 to 4.2 operations
> per core per cycle at the nominal (2.66 GHz, non-TurboBoost) clock rate.
> (DGEMM is double precision, but I am not familiar enough with scientific
> computing or with the Nehalem implementation of SSE to know why it is
> four operations per cycle rather than two -- is it because double
> precision counts as two FLOPs or is it because of multiple issue?)
> TurboBoost runs up to 2.93 GHz on this CPU, so it doesn't fit either the
> theoretical peak performance or the performance discrepancy very well.

Hi Michael,
I read http://www.intel.com/support/processors/sb/cs-023143.htm
and TurboBoost on 920 is 2.80GHz.
> why it is four operations per cycle rather than two

It's bit strane to me as well. but I did dgemm operation with m=k=n case and 
in this case, flop count would become 2n^3 + 2n^2 (even 2n^3 is okay). 

thanks
-- Nakata Maho http://accc.riken.jp/maho/ , http://ja.openoffice.org/ 
   Nakata Maho's PGP public keys: http://accc.riken.jp/maho/maho.pgp.txt