[flotus1]

Lineup
It has come to my attention that there is no source to get a quick overview on the current lineup of Intel processors for socket 2011-3, specifically the Broadwell-E and Broadwell-EP CPUs. And to be honest I was not aware of every single option that might be interesting from a CFD point of view. So here is my attempt to put as much relevant information as possible into a single table.
Some CPUs are missing because they are not freely available (e.g. exclusive for some OEMs) or rather irrelevant for CFD. The "all core turbo" frequency in the last column is -to my best knowledge- the frequency for execution of AXV code.





An attempt to rate the performance
Since all the processors above have the same architecture, it is possible to rate their relative performance based on the specifications. A very simple model to do this is Amdahl's Law. It makes the assumption that when N cores instead of one are used, the additional cores are not N-times faster. Instead, you see diminishing returns when using more cores. This can be caused for example by portions of the code that were not parallelized or by running out of memory bandwidth to keep the additional cores fed with data. The model is not perfect, but adding more complexity will not help making things clearer.
There are two more factors we have to take into account: Memory speed and cache per core since these factors are not equal along the lineup. So we make the assumption that less memory speed translates into less CFD computing power with an efficiency of 75%. For example: 11% less memory speed result in a penalty of 8.3%. More cache per core is given 20% efficiency, so 50% more cache per core give a bonus of 10%.
The result is a number that can be used to estimate the relative performance of these CPUs.
Note that for the dual-socket CPUs, twice the number of cores was used for Amdahl's law.
While we are at it we can try to rate the price/performance ratio aswell. We simply take the performance number and divide it by the cost for one or two CPUs plus the "typical" cost for the rest of the workstation. I used 2000$ for a dual-socket workstation and 1300$ for a single-socket system.
Without further ado, here are the results for five different scaling efficiencies. All numbers are normalized to the lowest value:



Now all you have to know is how does your software scale. An efficiency of 99% is highly unlikely for a CFD code, at least when using a very large number of cores. This is what is usually referred to as "memory bandwidth bottleneck". Which is why the CPUs with very high core counts are usually not beneficial for CFD or at least not the best use of your money. You should probably focus on the range 95%-98%.
To back up this claim we can take a look at this whitepaper from HP: http://www.peraglobal.com/upload/con...2555_13361.pdf
As a mean value for several Fluent benchmarks, they report a speedup of ~16 for a single node with 32 cores. This translates to a scaling efficiency of ~96.8%.
The CFX benchmarks show a speedup of ~18 on a single node with 24 cores which results in a scaling efficiency of 97.8% for the model of Amdahl's law.



Questions and answers:
Q: So which one is the best processor for CFD
A: It depends. The answer will usually be one of the processors with medium core counts and a high frequency. But you also have to factor in licensing issues. If all you have is parallel licenses for 8 cores, buying a 24-core workstation is usually not the best use of your budget.
Q: Why are some processors missing?
A: I focused on processors you can buy off the shelf. The quad-socket processors are also missing because you will have a hard time finding suitable motherboards, cases and power supplies as a normal customer. And at least from my limited experience with quad-socket, scaling is not always as good as you would expect.
Q: Why are the I7 processors even in this list? I heard that they are less reliable than Xeon processors.
A: This is not true. They are the same processors with a few features deactivated. For example, they do not officially support ECC memory. But on the other hand they are unlocked and can use faster memory which makes them an interesting alternative, especially for CFD.
Q: Isn't this about a year too late? These processors have been around for a while now.
A: Maybe, sorry about that. But they will remain your only option for at least a few more months.

Disclaimer: I take no responsibility for errors in the tables above. Please let me know if you find any.
Additional sources:
http://ark.intel.com/products/family...Family#@Server
http://ark.intel.com/products/family...ssors#@Desktop
https://www.microway.com/knowledge-c...ep-processors/
http://hexus.net/tech/news/cpu/91676...masked/?page=3