Oh, you are completely right here. My observation (colored by guessing how it works) is that every CPU you allocate to rack immediately goes up to 100% usage. Or close to it. Even if VCV isn’t doing anything. In contrast to must audio software where you can tell it to use all your cores, but it will only use as much as it needs. On my 4 core if I allocate even 3 to the engine and set them to realtiem my computer gets unresponsive.
I suspect it’s maybe a side effect of Rack doing processing one sample at a time (which is a great thing for a modular). Can’t help wondering if it could be done with less “wasted” CPU though.
That said, if you nave an “n-core” machine, isn’t it OK to give rack n-2 of the cores? I believe (but haven’t really verified) that more cores do help VCV quite a bit, but you need to be careful.
But, usual caveat, I don’t use back patches on Rack much. I tend to make small patches to test my own stuff.