Thanks to Joe Chang w/ Solid Quality for this great in-depth answer:
Due to the positioning from CPU vendors like AMD and Intel, and software vendors per socket licensing,
all favor going to multi-core from the price-performance perspective.
From the purely technical perspective, specific to AMD:
Each AMD Opteron processor (socket level) has 2 DDR(2) memory channels.
The difference between a system with one Dual Core Opteron and a system with two Single Core Opterons is that the the 2 socket system has a total of 4 DDR-2 memory channels.
So applications that are memory transaction intensive could favor the 2 single core system.
However, in the single Dual Core, memory is non-uniform.
Local memory is directly attached to the processor, a single 50-60ns hop for memory. In the the 2 Single Core system, memory is non-uniform. Some memory is local, some is remote, attached to the other processor.
In a two node system, the remote memory access is something like 90-100ns. There is also cache coherency traffic between the two nodes. There is cache coherency in the Dual Core, but its all on-die, with no bandwidth implications
In theory, AMD could put out a really fast single core Opteron, faster than a dual core, but they do not.
So there is no reason to evaluate single vs dual core. Just get the latest technology, which is currently Dual Core.
Quad Core Opteron is coming soon. If launch frequency is low, ie, below 2.5GHz, some applications may favor fewer faster cores than more slower cores. However, as AMD works out the Barcelona frequency issues, quad cores will be the correct solution (until 8 core chips come out)
--Joe Chang: JChang@SolidQ.com

Diana9/6/2007 5:27:26 PM

I've sent this question off to a few of the performance authors to see if they've seen any test results on this.
- Diana May

Diana9/6/2007 12:16:11 PM

You show the performance difference of a dual-core opteron vs. a single core opteron. But what is the performance difference of a dual-core opteron vs. 2 single core opterons ? In per performance per CPU, which is better, multiple single cores or single/multiple multi-core CPUs ?

DOUG8/7/2007 10:02:02 AM