Microsoft has released information on how to enable the Retpoline Spectre mitigation feature in Windows 10 October 2018 Update build 1809. Microsoft introduced fixes that caused a performance decrease in older Intel and AMD processors to mitigate Spectre vulnerabilities. Microsoft has been testing a new mitigation technique in Windows Insider Preview builds since build 18272. If you are using older Intel processors or AMD processors, you can boost the performance of Windows 10 by enabling this mitigation. For AMD processors and Broadwell Intel processors and older, the RSB’s behavior is predictable and this mitigation can be used.
Source: https://www.bleepingcomputer.com/news/security/boost-windows-10-performance-with-retpoline-spectre-mitigation/