Background. I am the author of an application that emulates a Tandy Color Computer (Motorola 6809). This app has been stable for five years.
Lately I have noticed some strange CPU boosting issues with the application.
The application is written for Linux and has been tested on both X64 and ARM64 platforms.
Recently on intel platforms the frame per second governor which has always been 60 FPS is now oscillating between 56 & 64.
I always keep old builds in my library and so launched a two year old working version and it too is exhibiting this same FPS fluctuating behavior.
Since my old executables have not recompiled themselves something must have changed with the kernel CPU scheduling. GUESSING!!!
I then tested this on a clean build of Ubuntu 22.04 but on an AMD platform.
The FPS counter is rock steady on 60 fps. Both systems are Ubuntu 22.04 with the kernel 6.5.
On the AMD system I then noticed the emulated motorola 6809 frequency would not raise to the requested frequency (unless it was set very low).
It was at this point I noticed my app on the AMD system was not causing the CPU to boost away from the minimum base clock frequency, regardless of how much load I created in the emulator. The system is a laptop and is on AC power with cpufreq-info showing the cpu governor is set to "Performance".
On the Intel system monitoring the application in htop shows the app is multi threaded and the CPU emulation thread was running at 109%+. On the AMD system it too shows it is multi threaded but the CPU emulation thread would never exceed 99%.
I have to admit this is the first time I have used an AMD system for development but I was surprised at this difference.
I would appreciate any ideas on how I might investigate these issues further.
Issue 1 - fluctuating FPS on IntelIssue 2 - refusing to boost on AMDUpdate: I transferred the old and new executables to another desktop system running Ubuntu 22.04.03 but with kernel 5.15.0.94 and everything is working as expected.
I'm leaning further to a recent change in the kernel!!!