I have an applet in my Gnome Panel which shows me the current load of my CPU. This is important on my laptop because it's a slightly older machine, and so knowing when I should let it finish one task before starting another stops me from getting frustrated with it.

However, sometimes when the CPU is maxing out at 100%, and stays there for a while, it can be an indication that something has gone wrong and maybe I should kill the process.

However, I've noticed over years of using Ubuntu that the System Monitor never really informs me what's going on.

Take for example, this screenshot (the interface is in Japanese, but that shouldn't change the problem):

Just above the System Monitor itself is my panel applet, where the box filled with green just to the right of the battery indicator is also indicating 100% CPU usage.

Now look at this image:

Nothing is using any more than 7% of the CPU.

This seems to be very frequently the case - I dare say almost always - that when the CPU is maxing out, I can never see what is actually using those CPU cycles.

I have tried using HTOP at the command line as well, but the results are the same.

Why does the System Monitor always show me 100% CPU use in general, but never more than a few % when I look at the total of specific processes?

What am I supposed to do when I want to figure out what is using so much CPU time, should I want to to kill runaway processes, or at the very least know what the process is?