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Total CPU Cores vs Physical CPUs

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January 17, 2012 7:47:08 PM

Hello,
I'm looking at two server models (different manufacutures). Manufacturer #1 offers a 4 CPU (6 Core per CPU) system for a total of 24 cores. Manufacturer #2 offers a 2 CPU (12 Core per CPU) system for a total of 24 cores. Mfct#2 has a .2GHz advantage in speed. What advantages / disadvantages do you see? Both have the same number of cores.
For starters I see two. (1) Mfct#1 will probably generate more heat and consume more power, (2) Mfct#1 has more redundancy built in. If one of Mfct#2 CPUs fails - half the computing power fails with it.

Thanks
a c 850 à CPUs
January 17, 2012 10:34:28 PM

If one CPU fails the whole system fails! You are probably right about the power consumption though.
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a c 190 à CPUs
January 17, 2012 10:59:07 PM

Redundancy with physical CPUs is redundant, their random failure rate is quite low, their DOA rate makes up most of the failures, and as rolli said, if one CPU fails the whole system fails.

What CPUs are you looking at? What do you intend to do with your system? If the 4 CPU system is xeon CPUs with hyper threading you will actually have the ability to run twice as many threads which could be quite useful. Its also important to know what you will be using it for as some CPU line ups have better performance with certain tasks than others.
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a b à CPUs
January 17, 2012 11:58:04 PM

Failure rates on CPUs is very low, so unless your use-case is very critical then reliability is not nearly as important as performance/dollar or performance/watt. It's hard to make a solid recommendation based off such vague details.
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January 18, 2012 1:28:47 PM

Thanks for the replies - Looking at this from another perspective:
All else being equal - Would 4 CPUs with 6 cores per cpu (24 cores total) be equal

in processing power to 2 CPUs with 12 cores per cpu (24 cores total)?
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a c 850 à CPUs
January 18, 2012 1:30:05 PM

If they are out of the same CPU family they should.
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a c 79 à CPUs
January 18, 2012 1:50:05 PM

although shuffling data between sockets will be slower than between cores, so if you have a 4 socket system you are twice as likely to have this type of traffic than on a two core system.

If memory controllers are on-die then you'll have twice as many memory controllers and therefore bandwidth, but you'll have 4 segemented memory areas (or areas with slow transition between them) vs just 2 areas.
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a b à CPUs
January 18, 2012 2:45:45 PM

marcus65 said:
All else being equal


This is really the active term here. It's difficult to say whether one would be better because it would be virtually impossible to design 2 hexacore CPUs that are exactly equivalent to a single 12 core CPU. Even if you could the prices wouldn't be matched because it would likely cost more to buy 2 chips than 1.

If you assume everything is EXACTLY equal then it comes down to whether you'd prefer having lower failure rate or lower failure impact.
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a b à CPUs
January 18, 2012 3:17:05 PM

13thmonkey said:
although shuffling data between sockets will be slower than between cores, so if you have a 4 socket system you are twice as likely to have this type of traffic than on a two core system.

If memory controllers are on-die then you'll have twice as many memory controllers and therefore bandwidth, but you'll have 4 segemented memory areas (or areas with slow transition between them) vs just 2 areas.

I agree, if you have 4 separate CPUs with 4 memory controllers, you will have more memory bandwidth, but the data would also have to jump through more hoops with 4 CPUs than with two so energy used and latency would be greater.

Certain applications will be faster with the 4 CPU system if memory bandwidth(or total memory amounts) is a concern while other applications will be just as fast or faster on the 2 cpu system while using less energy.

Cooling would be a little bit easier on the 4 CPU system, since TDP per CPU should be lower if all else is equal. More heat has to be removed from the case, but each heatsink is removing less heat from its respective CPU.
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