CPU-Z shows 8 cores, but 4 of them are stopped

I am using CPU-Z to test basic things about the J7. It reports an Exynos Octa 7580, 8 cores, 8x ARM Cortex-A53 @ 1.5GHz, r0p3, 28 nm.

At all times that I checked, only cores 0-3 are active, and cores 4-7 are stopped. Power saving is disabled.

Is there any way of activating all cores?

Is there any way of at least seeing all of them active, for testing purposes?

I have found a few posts around (here and here) mentioning that it may be the way the phone + OS kernel keep temperature in check, but I am not sure it applies to J7, and if so, how to circumvent it.

PS:

I find some times that my J7 is sluggish, so I wonder why would it have 4 processors idling if they could work (assuming the causes are processing several apps, which could be tackled by assigning different processors).