[nSLUG] Atom vs Xeon

Stephen Gregory nslug at kernelpanic.ca
Fri Apr 30 11:45:33 ADT 2010

George N. White III wrote:

> See: <http://www.extremetech.com/article2/0,2845,2362982,00.asp>

Interesting article.

> "The large power cost of the Xeon is not justified by relatively modest
> increases in
> sustainable throughput," the researchers concluded."

The is an odd conclusion given that the researchers found that even
large numbers of Atom processors could not run the tested work load
effectively. (Microsoft's Bing search engine. see the paper for details.)

 "The problem, the researchers concluded, is that the Atom is
  fundamentally weaker in processing the neural network algorithms that
  assign page rankings, even at a minimum load of 10 queries per


 "The Atom's advantages were also mitigated by the fixed power
  requirements of a data center. To match the throughput of a datacenter
  full of Xeons, the researchers found that seven times as many Atoms
  would be required, increasing the total power consumption to three
  times that of the Xeon and well above a typical power budget."

On paper the Atom is more efficient. In reality the Atom simply can't do
the work of the more powerful Xeon. The Atom is an in-order processor
designed to be idle most of the time handling user loads with a few
threads. The Xeon is an out-of-order processor designed to be fully
loaded all the time by many threads.

> "By integrating up to eight Diamondville cores into a single chip and
> building a system
> with two sockets, amortization once again highlights Atom efficiency.
> As per our computed
> cost... an integrated low-power multi-processors would be competitive
> with a cost and
> power efficiency advantage of 1.03× and 2.3× over the Xeon."

I believe this is a naive assumption. In order to build an eight core
Diamondville cpu extra logic would need to be added raising the power

The idea has merit Sun's T2 (Niagara 2) processor is 8 low power in
order cores. The T2 is an efficient processor provided it is fully
loaded with 64 threads. It is a great file and web server. However the
L5420 Xeon used in the paper is faster for less power. The new Nehalem
processors are much faster for less power.


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