Yes, the governor can play a role. It's visible to the user, which is the point. Also, the ondemand governor is actually irrelevant to the article as the S821 and S670 used the interactive and schedutil governors respectively, and the i5-6600K was using speed shift.
I think we're disagreeing because I really don't care about how fast a CPU could pull off frequency transitions if it's never observable to users. I'm looking at how it's observable to user programs, and how fast the transition happens in practice.
> Processor still performs periodic sampling...
Same as the above, that's not the point of the article. I'm not measuring "what could theoretically happen if you ignore half the steps involved in a frequency transition even though a user realistically cannot avoid them without serious downsides" (like artificially holding the idle voltage high and drawing more idle power, as in the Piledriver example)
> In any case, a multi-millisecond delay in switching frequency isn't because the processor is waiting for the voltage to increase.
Yes, there are other factors involved besides the voltage increase. I never said it was the only factor, and did mention speed shift taking OS transition commands out of the picture (implying that requiring OS commands does introduce a delay in CPUs without such a feature).
If you want to test how fast a CPU can clock up, without influence from OS/processor polling, please do so and publish your results along with your methodology. I think it'd be interesting to see.