Comment 14 for bug 1917813
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#14 |
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a60fb26
(Get the code!)
Created attachment 294275
Graph of load sweep at 200 Hertz for various idle states
> Now, actually I can not prove if the idle state 2 part
> is a cause or consequence, but it never happens with it
> disabled, but at the cost of significant power.
idle state 2, combined with the timing window, which is much much larger than previously known, is the cause.
The CPU load is increased to max, then decreased. As a side note, there is a staggering amount of hysteresis and very long time constants involved here.
If one just sits and watches turbostat with the system supposedly in steady state operation, HWP can be observed very gradually (10s of seconds) deciding that it can reduce the CPU frequency, thus saving power. Then it has one of these false frequency drops, HWP struggles to catch up, raising the CPU frequency as it does so, and the cycle repeats.