[Brick] CPU stuck at 2000 MHz on a fresh install of 6.11.1

[pvaibhav]

Steps:

1. Install NextUI 6.11.1 on a freshly formatted SD card. Insert and reboot.
2. Copy some games and start one of them.
3. Enable Debug HUD from the minarch Frontend options.
4. Observe the cpu is stuck at 2000 MHz.
5. Observe the CPU Speed set in Frontend options is (by default) Auto.

Expected:

CPU should be dynamically scaling.

Solution:

Change the CPU Speed to Performance and then back to Auto. After the minarch menu is closed, notice the CPU speed is now dynamically scaling as expected.

Possible cause:

I guess something is not being properly initialised either in minarch or the main menu system.

Could be related to #705

[pvaibhav]

Root cause

On startup, minarch calls setOverclock(1) to select Performance mode for fast startup. However this function writes overclock = 1. Later after init, minarch calls setOverclock(overclock), but when there is no saved setting for the console, nothing resets this variable back to 0 (i.e. Auto). So an unsaved config (e.g. on a fresh install) causes a silent change of the CPU mode to Performance even though the UI still shows Auto.

Solutions

Either remove setOverclock(1) because the Auto governor, which should already be active before game launch (main menu screen) will handle cpu upclock just fine, let the scaler do its job. Then console-specific config may override it as per the user's saved choice, or stay at Auto if nothing has been overridden by the user.

Or, instead of setOverclock(1), directly set performance mode via PWR_setCPUSpeed(CPU_SPEED_PERFORMANCE).

I prefer the former, although this limits the CPU to one step below the max overclocked rate.

Need another opinion to decide.

[huyhoang160593]

If we can benchmark the time it take when using auto and overclock that should be nice

[pvaibhav]

Timed Advance Wars start-up on mGBA 4 times with stock 6.11.1 code, skipped the first to let caches warm up:

[INFO] total startup time 940ms
[INFO] total startup time 945ms
[INFO] total startup time 940ms

Same but with 'auto' scaler in both MinUI.pak/launch.sh and minarch:

[INFO] total startup time 1081ms
[INFO] total startup time 1071ms
[INFO] total startup time 1078ms

Pretty much exactly as expected, 10% reduction in clock speed and 10% increase in startup times.

[pvaibhav]

With option #2 (keeping performance mode without clobbering overlock variable), the CPU speed is reset to auto midway through the initialisation. So the startup time is somewhere in the middle:

[INFO] total startup time 979ms
[INFO] total startup time 1015ms
[INFO] total startup time 1003ms
[INFO] total startup time 976ms
[INFO] total startup time 976ms

And if I move the cpu speed reset to the very end just before the "total startup time" is calculated, I get the fastest results:

[INFO] total startup time 923ms
[INFO] total startup time 900ms
[INFO] total startup time 896ms
[INFO] total startup time 939ms

So I am revising the PR to this last method. It doesn't shake up much but solves the bug without any performance regression, in fact a small performance gain.