Operating system: Windows 7 pro 64bit
CPU: 2*Intel Xeon e5-2696v3
Short description of error
When i render, Cycles wont use both NUMA Nodes (or CPU Groups) but only one. Even if i change from "Auto detect" to "Fixed" and fill in "72" inside the Performance-Tab, it spawns 72 Buckets but will actually use only 36 CPU Threads. While the auto detect option also didnt work in 2.79, the "fixed" parameter worked and used all 72 Threads for rendering.
Since this occurs only on this machine and not my second one (only 48 threads), my guess is that this is an issue with Windows CPU Grouping that will split everything that exceeds 64 Threads into Groups. If a software is not aware of this, they can only use one NUMA Node (or cpu Group). In my case that would be exactly 36 Threads.