Users may have been following Wendell from Level1Tech’s battle with researching the reasons behind why some benchmarks have regressed performance on quad-die Threadripper 2 compared to dual-die configurations. Through his research, he found that this problem was limited to Windows, as cross-platform software on Linux did not have this issue, and that the problem was not limited just to Threadripper 2, but quad-die EPYCs were also affected.

At the time, most journalists and analysts noted that the performance was lower, and that the Linux/Windows differences existed, but pointed the finger at the reduced memory performance of the large Threadripper 2 CPUs. At the time, Wendell discovered that removing CPU 0 from the thread pool, after the program starts running, it actually regained all of the performance loss on Windows.

After some discussions about what the issue was exactly, I helped Wendell with some additional testing, by running our CPU suite through an affinity mask at runtime to remove CPU 0 from the options at runtime. The results were negative, suggesting that the key to CPU 0 was actually changing it at run time.