8 cores and above - Is the race worth it?
You may note that Engineers at Sandia National Laboratories did simulation of 8, 16 and 32 cores, and have opined that performance of multi-core machines would level off or even decline beyond 8 cores,due to limited memory bandwidth.
Read more here.
At the heart of the trouble is the so-called memory wall—the growing disparity between how fast a CPU can operate on data and how fast it can get the data it needs. Although the number of cores per processor is increasing, the number of connections from the chip to the rest of the computer is not. So keeping all the cores fed with data is a problem. In informatics applications, the problem is worse, explains Richard C. Murphy, a senior member of the technical staff at Sandia, because there is no physical relationship between what a processor may be working on and where the next set of data it needs may reside. Instead of being in the cache of the core next door, the data may be on a DRAM chip in a rack 20 meters away and need to leave the chip, pass through one or more routers and optical fibers, and find its way onto the processor.
I would really love to run the MT tests that would show the performance at 6 and 8 core. Searching ...