[cluster-l] Single- vs. Dual- vs. Quad-core CPUs

[Nils Oberg]

Hi Jim,

Thanks for your response.  I should probably describe the 
problem.  Our application is a computation fluid dynamics (CFD) 
code.  My understanding of CFD codes is that they are primarily 
memory bound.  Since the domain to be modeled is broken up into 
chunks, during the course of a time-step in the simulation a large 
number of messages (not necessary large amounts of data) are passed 
between processors.

We're trying to decide between the following:

uni-processor quad-core Xeon 4 GB RAM ($2,300 / node)
dual-processor quad-core Xeon 16 GB RAM ($5,800 / node)
dual-processor quad-core Xeon 8 GB RAM ($4,600 / node)
dual-processor dual-core Xeon 8 GB RAM ($3,800 / node)
dual-processor dual-core Opteron 8 GB RAM ($3,200 / node)


At 16:12 1/22/2007, Jim Phillips wrote:
>Are you limited by memory bandwidth or clock speed?  All of those 
>cores share the same memory bandwidth, but the clock speed is almost the same.

I really don't know which is a limiting factor.  I'm guessing it is 
memory latency (is that clock speed?) more than anything.

>Is memory an issue?  How much memory do you need per node and per 
>core? If you can use shared-memory within a node then you can add 
>cores without adding extra memory.  Otherwise you may need to use 
>larger memory chips to fit enough memory into the node.  Quad-core 
>is more flexible if you only need more memory on occasion since you 
>can drop down to one core per node.

The programs currently don't use shared memory.  I think would be 
fairly difficult to recode the software for shared memory, as it is 
using external libraries (Petsc, Parmetis) that rely on MPI.

The newer Intel CPUs (Xeon 5000 series) require fully buffered 
RAM.  I've read that FB RAM has both higher latency and lower 
bandwidth.  Does this mean that, respectively, requests from the CPU 
take longer, and the amount of data transferred is smaller?

A second question: The memory clock speed should be 50% of the CPU 
front-side bus speed, correct?  In other words, I shouldn't get 533 
Mhz memory with a 1333 Mhz FSB?

Thanks for your help!

Nils


>On Fri, 19 Jan 2007, Nils Oberg wrote:
>
>>Hello,
>>
>>Our group is going to purchase a small cluster.  I'm trying to decide
>>if each node in the cluster should have dual- or quad-core
>>CPUs.  Does anyone have any advice for how to benchmark?  Or other
>>resources that might help me get started?
>>
>>As an FYI, I noticed that NCSA is building a new cluster
>>(http://www.ncsa.uiuc.edu/UserInfo/Resources/Hardware/Intel64Cluster/)
>>that has dual-socket quad-core compute nodes for a total of 8 cores.
>>
>>Nils
>>
>>
>>
>>--
>>Nils Oberg, Research Programmer
>>Civil & Environmental Engineering, University of Illinois at U-C
>>phone: 217-333-8365, web: http://vtchl.uiuc.edu
>>
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>>cluster-l mailing list
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>
>--
>Nils Oberg, Research Programmer
>Civil & Environmental Engineering, University of Illinois at U-C
>phone: 217-333-8365, web: http://vtchl.uiuc.edu