The Intel Xeon E5 v4 Review: Testing Broadwell-EP With Demanding Server Workloads

HPC: Fluid Dynamics with OpenFOAM

Computational Fluid Dynamics is a very important part of the HPC world. Several readers told us that we should look into OpenFOAM, and my lab was able to work with the professionals of Actiflow. Actiflow specializes in combining aerodynamics and product design. Calculating aerodynamics involves the use of CFD software, and Actiflow uses OpenFOAM  to accomplish this. To give you an idea what these skilled engineers can do, they worked with Ferrari to improve the underbody airflow of the Ferrari 599 and increase its downforce.

We were allowed to use one of their test cases as a benchmark, however we are not allowed to discuss the specific solver. All tests were done on OpenFOAM 2.2.1 and openmpi-1.6.3. The reason why we still run with OpenFOAM 2.2.1 is that our current test case does not work well with higher versions.

We also found AVX code inside OpenFoam 2.2.1, so we assume that this is one of the cases where AVX improves FP performance. 

As this is AVX code, the clock speed of our Xeon processors can be lower than Intel's official specifications, and turbo boost speeds are also lower. Despite the fact that on Broadwell the only cores that reduce their clock when running AVX code are the AVX-active cores themseves (the others can continue at higher speeds), OpenFOAM does not run appreciably faster on the top of the line Xeon E5 v4 than it did on the E5 v3.

It is not as if OpenFOAM does not scale: 22% more cores delivers 13% higher performance (E5-2699v4 vs E5-2695v4). No, our first impression is that the new Xeon v4 needs to lower the clockspeed more than the old one. The official specifications tell us that both the Xeon E5-2699 v4 and v3 should run AVX code at up to 2.6 GHz with all cores enabled. The reality is however that Broadwell runs at a lower clock on average.