Physical CPU? or multicore?

Question

I've asked the same question in Oracle-l...For those who are not in the mailing list.. here it goes...
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With the release of Intel (Nehalem) 5500 series, which is 45nm and I believe also supports multicore and hyperthreading. There are some things going on my mind..So from a single socket (Nehalem), quad core and HT enabled. You could see 8 processors when you do "cat /proc/cpuinfo"
But, from the performance perspective. Which is better?
Having 8 physical CPUs? Or Having 1 Physical CPU with quad core and HT enabled?
(Well, we know the license implications of 8 physical CPUs).. :)
But for the performance engineers and capacity planners. I'd like to hear your opinion.
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- Karl Arao
karlarao.wordpress.com

Answer 1

First, I would be happy with one multi-core CPU instead of multiple separate single core CPUs. So quad core is good for me. There are several caveats to this, related to things that would impact the effective performance of each core. So things like clock speed, cache sizes - both on chip and off chip - and some other things are all important. But assuming the clock speed is no slower, and the cache sizes no smaller too, then multi-core is generally good. You get the throughput of 4 CPUs for the price of 1, and it only needs the space of one on a motherboard. Hence all the costs of the system are less.
Second I would avoid any virtualization within the cores completely. Whether it is Hyper-Threading or Sun's Chip Multi-Threading (CMT) or something else. Virtualization of CPU cores hides what is really happening inside, and decreases single thread performance. Clearly each core can only ever execute one instruction at a time, from one thread at a time. So although any internal multi-threading within a core is sharing the core between multiple threads for greater overall efficiency, each individual thread actually gets executed on the core less often due to the sharing which results in slower performance per thread.
Yes, I would take a quad core CPU with 4 real, separate execution cores. But I would disable any virtualization within the cores that make each real core look like multiple virtual CPUs. Oracle will charge you by the number of CPUs visible to the operating system. With virtual CPU cores you will need to buy Oracle licenses for each of them. Disabling virtualization means that you get better performance and only need to buy the minimum number of Oracle licenses.
John Brady