32 bit Ubuntu guest must be indicated as Ubuntu 64 Bit to avoid 4X CPU slowdown

[kazinator]

One of my VirtualBox machines is an 32 bit Ubuntu 18. I created it some five or six years ago, at the same time as getting a new computer. Everything is 32 bits in that VM: kernel and userland. "uname -a" reports the kernel's arch as i686.

I had always been slow, and I blamed the hardware.

Recently, I discovered that the performance on CPU-intensive tasks like compiling improves 4X (four times) if I change the OS designation from "Ubuntu 32 Bit" to "Ubuntu 64 Bit".

How I discovered this may be worth mentioning. I had neglected updating VBox for a number of years. Suddenly, I jumped from like 6.1.4 to 7.1.6. After the upgrade, I used the new VBox to resume virtual machines that had been suspended by the old VBox. That Ubuntu 18 machine spontaneously showed the 4X speedup! Unfortunately, the benefit was short-lived. When it was restarted, the bad performance returned, and after that I searched persistently for a configuration change that would restore the good performance, and hint at the root cause.

I don't have any files to attach, and my problem is solved from my end; this is more of a heads up that there is this issue.

I have a few other 32 bit machines, like a Mac OS 7.1.4 one and Solaris 10; they are also similarly slow. I will experiment to see whether the trick can be applied to them.