AMD’s latest Ryzen processors performance hit by Windows 10 Scheduler bug

After four years and more than two million engineering hours of development, AMD finally announced the launch of AMD Ryzen 7 desktop processors. AMD designed these processors for PC gamers, creators, and enthusiasts with 8-cores, 16-threads, and the new AM4 desktop platform. As per AMD, their flagship Ryzen 7 1800X is the world’s highest performing 8-core desktop processor, and Ryzen 7 1700 is the world’s lowest power 8-core desktop processor. AMD also demoed that Ryzen 7 1800X outperforms a similarly configured 8-core, 16-thread Intel Core i7-6900K in Cinebench R15 multi-threaded and Handbrake-based video transcoding. The AMD Ryzen 7 1800X costs $499, less than half of what Core i7-6900K costs in the market today.

Unfortunately it seems Windows users on the latest version of Microsoft’s desktop OS will not be able to get the maximum benefit from the high performance, good value solution.

A bug has been discovered in the Windows 10 Scheduler which limits the performance of AMD Ryzen CPUs. The issue is due to the difference between how Windows treat threading between Intel and AMD processors.

For Intel hyperthreading it appropriately prioritizes the main thread and gives secondary threads lower priority. With AMD processors it treats all the threads as equal, meaning lower priority tasks are treated the same as higher priority tasks and overall performance suffers.

Another bug also incorrectly identifies the amount of cache available per thread, with the Windows 10 Scheduler thinking each thread has 136 MB of RAM rather than the actual 20 MB available in the L2+L3 cache combined.

At present the issue is only believed to affect Windows 10. Windows has had scheduler issues in the past, so we are sure a solution is only a software update away.

In the mean time users can disable SMT in the BIOS to improve performance in gaming, but for more multi-threaded work it may be better to leave it enabled.

Read more detail about the issue at WCCFTech.

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