I have an I7-8750H and currently have a dual boot machine with Win10 and Ubuntu 18.04 with the 4.18.8 kernel.
When I stress test all cores of the cpu in windows it reaches 3.9 GHz which is as it should, but when i stress test in Ubuntu, the cores only reach 2.5 GHz.
I have tried changing the scaling governor but doesn't change the outcome.
i7z says:
Socket [0] - [physical cores=6, logical cores=12, max online cores ever=6]
TURBO ENABLED on 6 Cores, Hyper Threading ON
Max Frequency without considering Turbo 2307.32 MHz (100.32 x [23])
Max TURBO Multiplier (if Enabled) with 1/2/3/4/5/6 Cores is 41x/41x/40x/40x/39x/39x