From Wccftech:
A newly discovered bug in Windows 10’s scheduler has been found to be negatively affecting performance of AMD Ryzen CPUs. The bug has been confirmed to affect all Windows 10 versions but not Windows 7. It’s not clear yet if Windows 8.1 is affected.
Ryzen processors are AMD’s first ever to feature simulatenous multi-threading technology. [...] Intel’s hyper-threading technology works in a very similar fashion. [...] In best case scenarios SMT provides about 20-30% of additional throughput give or take in both Intel’s latest Skylake microarchitecture and AMD’s Zen microarchitecture.
Windows 10′s scheduler correctly identifies Intel’s hyper-threads as lesser performing than principal core threads and schedules tasks in a way that’s takes advantage of the additional throughput without negatively impacting performance. Unfortunately the scheduler currently is not able to differentiate principal core threads from virtual SMT threads with Ryzen and in fact sees 16 thread Ryzen 7 processors as processors with 16 physical cores with equal resources per thread.
Because it does not give any preferential prioritization of scheduling tasks to primary threads over SMT threads like it does on Intel platforms, a massively larger percentage of tasks can and do end up getting scheduled for a virtual SMT thread rather than a principal core thread. Resulting in significant artificial performance degradation.
First things first, we’ve been informed that AMD has become aware of the issue. I’m sure they must’ve had some stern words for Microsoft over this mishap. The company has been pushing hardware manufacturers to adopt its brand newest OS for years. So it must’ve left a bitter taste in AMD’s mouth after embracing Microsoft’s Windows 10 push for it to be rewarded with poor hardware support. With that being said, it’s safe to assume the pair are actively working together to get this issue resolved.
Again, this is a bug that only affects Ryzen PCs running Windows 10... which is all of them, because AMD is only supporting Ryzen for Windows 10. I wonder if they're re-thinking that wisdom of that decision, yet? Especially since Ryzen benchmark scores were puzzlingly low, something that AMD were having trouble explaining. Well, here's the explanation: Microsoft royally fucked them over, and AMD should be planning legal action. At the very least, AMD should be looking to get out of that Windows 10 exclusivity side-deal, now that Microsoft's incompetence has resulted in wave of coverage like "Gaming benchmarks on Ryzen are a critical mess," and "Gaming isn't a strong point for AMD's fledgling architecture."
GG, Microsoft. GG.