ZGPAX S5 CPU tweaking (this could also be applicable to other phones)
https://www.dr-lex.be/hardware/china_zgpaxs5_review.html

The tweak works in two steps:
Step 1: set the system-wide CPU configuration with an app like No-Frills CPU Control to a power profile that is as low as possible, but good enough for most apps.
Step 2: use Per-App Modes to change the power profile for specific apps: lower for really simple apps, higher for demanding apps. Treat system apps separately to decouple them from the other tweaks.

Mind that slowing down the CPU will cause it to run longer for the same number of cycles required to finish a task, and in theory there would be no net energy savings. In practice this is not true: the CPU will typically be configured to run at a lower voltage when the frequency is lower, and a lower voltage does result in net energy savings (P = C*f*V^2).
However, for the ZGPAX S5 the main idea is to avoid the apparent bug in the default CPU governor that causes the CPU to remain stuck in a high-power state. Even if this would not work, the tweaks will make it less likely that the phone heats up for no good reason.


===System-wide setting (set with No-Frills CPU Control):===
governor=ondemand, min=250MHz, max=500MHz.
This will act as a default for all apps that do not have a profile in Per-App Modes. Feel free to experiment with other governors and frequencies. Using powersave 250MHz might also work, but I prefer to have a little extra margin.

===Per-app modes configuration:===
Create at least three profiles:
The minimum CPU speed is always 250MHz.

1. "System": governor=hybrid, max=1001MHz.
I am being conservative here, using the original ZGPAX system parameters. I assume that other parameters might cause problems. Works fine for me, but you can try other parameters at your own risk.

2. "Powersave": governor=powersave, max=250MHz
If you decide to set your system-wide parameters like this, then this profile is not needed. However, it is useful to have it if you would change your mind.

3. "Power": governor=ondemand, max=1001MHz
This provides the most responsive performance, but also has a risk of quickly eating through the battery.

You can create a fourth "Medium" profile with ondemand 667MHz for those apps of which you suspect that they could use a little more than 250MHz.

===Per-App Modes assignments:===
1. System profile:
Android System
APKInstaller
Atci_service
Bluetooth
CellConnectionService
com.android.provision
com.android.sharedstoragebackup
com.mediatek
com.mediatek.omacp
Common Data Service
DataReg
EngineerMode
Google Play Services
Location Engineer Mode
MTK Android Suite Daemon
MTK Thermal Manager
Package Installer
Phone
Phone/Messaging Storage
Pico TTS
System UI
USIM Toolkit
YGPS

2. Powersave profile:
Calculator
Calendar
com.szjingkante.actitivy
Contacts
File Manager
GMail
Messaging
Settings

3. Power profile:
Browser
Camera
Gallery
HTML Viewer
Maps
Video Player