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RYZEN thoughts?
Author:  Date: 2017-03-16 08:23
It's not clear to me that "compiler shenanigans" are responsible for the difference - which does vary quite markedly between games, and even between different APIs on the same game (eg. DX12 and Vulkan is relatively much worse for Ryzen than DX11 and OpenGL, which is the opposite of what you'd expect from an ordinary CPU bottleneck).

What we do know is that communication between CCXes (each of which carries 4 cores) is somewhat more constrained than communication within a CCX; they are linked by the Infinity Fabric which runs at a speed tied to the memory clock, whereas everything within each CCX runs at core clock speed. Games tend to have a lot of producer and consumer threads which communicate voraciously, and they generally don't achieve full core utilisation on a CPU as highly multithreaded as Ryzen 7, so Windows further complicates matters by migrating threads randomly from one core to another, often *between* CCXes. Productivity benchmarks appear to need relatively little communication between threads, and because all cores are fully utilised, Windows doesn't migrate threads between cores.

Hence productivity benchmarks can use Ryzen efficiently without needing to know about its quirks. Games need to be a bit more intelligent, and some of them apparently have intelligence tuned for Intel CPUs which unfortunately breaks on Ryzen. AMD posted something revealing about F1 2016 recently which illustrates this very neatly.

 
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