[AaronFriel]

Linux and Windows have both supported it, but use tends to be at the fringes on mainframe/datacenter machines that are validated for it and so those paths aren't tested on a very wide variety of hardware and running applications. And adding CPUs and memory is one thing but removing is another.

[kllrnohj]

CPU cores being hotplugged on & off was actually super common for a few years, and still is in a lot more devices than you'd expect.

It used to be a corner stone of power management on mobile devices. The Nexus 5, for example, would regularly run with just a single core online, hotplugging the other 3 off until hit with a load and then brought cores back online 1 by 1 as needed.

That behavior still is in some corners of the mobile world, but increasingly less so.

So the CPU hotplug path is as a result actually a lot more battle hardened than you'd expect, and a lot more consumer software than you'd think ran just fine in that setup without noticing.