AMD Ryzen Performance Negatively Affected by Windows 10 Scheduler Bug

..The principle thread executed by each core is allocated maximum instruction per clock throughput, i.e. maximum performance. The additional SMT thread on the other hand can only opportunistically leverage underutilized resources in a given core.

Intel’s hyper-threading technology works in a very similar fashion. Providing each “hyper-thread” with only a fraction of the resources available to the principle thread in any given CPU core. In best case scenarios SMT provides about 20-30% of additional throughput..

..Windows 10′ 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..

..We’ve seen similar issues in the past in the early days of Intel’s hyper-threading. It took some time and a few patches for it to work as intended and we imagine it’ll be the same for the all new Ryzen microarchtiecture. The good news is that Windows 7 does not exhibit the same issue and motherboard makers have thankfully released Windows 7 drivers for their AM4 motherboards. ..