[Beowulf] Athlon64 / Opteron test

[Cannon, Andrew]

> See answers indicated by the  >


Hi,

We're studying the possibility of installing a 64 bit testing node.

The main purpose is about getting impressions related to the performance
increase we would obtain in our particular scenario, computational fluid
dynamics.

In order to do the test, we have no doubt about the OS: Red Hat
Enterprise 3, but we are a bit confused about the harware of choice:

		Athlon64
		Opteron

As far as we know, Opteron has two main differences:

	- A wider memory interface (128 bit in front of 64)
	- A larger L2 cache memory (1 Mb)

Before doing any test, the questions are:

1)

 Which is the theoretical maximum performance gain using full 64 bit
architecture in front of 32 bit, taking into account that our
computations are done in double precision floating point using really
big matrices?

> I don't know about this one, but I think you expect about a 20% speed
increase over the equivalent 32 bit program on the Athlon 64. (i.e. compile
a code for 32 bit and then compile the same code for 64 bit and run them on
the same processor, and I've read that you get about a 20% speed increase).

2)

Is it nowadays the 64 bit solution using Linux ready for production?
If this is the case, which problems may we have to deal with in order to
compile and run our code in a full 64 bit environment?

> The Linux kernel has had 64 bit support for the Hammer family of
processors since before the processors actually came out. It is the
supporting programs and drivers that may cause problems. (We are having
display driver problems in X). gcc has got 64 bit support and the NAG
compilers are available for x86_64. (I received NAG Fortran v5 a couple of
days ago).

3)

Which is the most mature solution: AMD Opteron or Intel Itanium?

> It depends on what you want. Itanium is more mature, but doesn't give the
performance increase you would expect given the price. There is a  good
thread on the AMD forums that is looking at the relative speeds of Itanium
systems and Opteron systems running the same code. It can be found at
http://forums.amd.com/index.php?showtopic=14239 and compares a couple of
runs. It is not exactly benchmarking, but is a real world application.
Personally, I would choose the Opteron. Itanium is too expensive for the
performance you get from it.

> Also, some Athlon 64 processors have 1MB cache. The difference between the
Athlon64 and the Opteron is not that big. The major advantage of the Opteron
is that you can have it in dual, quad or 8 way systems.

Hope that helps.

Andy


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