Downtown Doug Brown » Why is my CPU usage always 100%? (Upgrading my Chumby 8 kernel part 9)
If you’re new to this series, I’ve been documenting the process I went through upgrading my old PXA166-based Chumby 8’s 2.6.28 Linux kernel to a modern 6.x version. Here are links to parts 1, 2, 3, 4, 5, 6, 7, and 8. At this point in the project, all of the main hardware peripherals were working great. I noticed something odd when running top though. The CPU usage was always really high, and it wasn’t obvious why.
That’s really weird! Why would top be using all of my CPU? It says 100% usr in the second line. Sometimes the usage showed up as 50% usr and 50% sys. Other times it would show up as 100% sys. And very rarely, it would show 100% idle. In that rare case, top would actually show up with 0% usage as I would expect. The 2.6.28 kernel did not have this problem, so it was something different about my newer kernel.
I started theorizing about what might be wrong here. My ideas were nothing more than wild guesses: maybe one of the drivers I got working earlier was totally monopolizing the CPU and making it look like other processes were using all the CPU. Or perhaps I was missing some kind of CPU idle support so the processor was stuck running at 100% at all times, never able to take a break. Maybe there was some power management support missing from the mainline kernel or something. I needed to figure out a way to narrow down the possibilities.
