看到「Bisected: The Unfortunate Reason Linux 4.20 Is Running Slower」這篇測試了目前還在 RC 的 4.20.0，可以看到 AMD 的效能沒有太大影響，但 Intel i9 的效能掉了很嚴重：
從說明可以看到有測出 30%～50%：
This ranged from Rodinia scientific OpenMP tests taking 30% longer to Java-based DaCapo tests taking up to ~50% more time to complete to code compilation tests taking measurably longer to lower PostgreSQL database server performance to longer Blender3D rendering times.
另外在其他 Intel CPU 上測試也發現不是只有 i9 有影響，低階的機器也是：
Those affected systems weren't high-end HEDT boxes but included a low-end Core i3 7100 as well as a Xeon E5 v3 and Core i7 systems.
透過 bisect 有找到是哪個 commit 造成的：
That change is "STIBP" for cross-hyperthread Spectre mitigation on Intel processors. STIBP is the Single Thread Indirect Branch Predictors (STIBP) allows for preventing cross-hyperthread control of decisions that are made by indirect branch predictors.
但這又是屬於 security patch，不太能關... 加上自從 Meltdown 與 Spectre 後，讓安全研究人員發現了全新的天地，之後應該只會愈來愈慘 :o