Thank you I was not aware of the security issues of hw.smt. Fortunately, things are fast enough without it, and I'm setting up a true multicore AMD system soon.
On my hypothesis about CPU usage competition, I was using "interrupt" in the sense that doesn't involve computers. For example, suppose that I first run something that outputs its processing as it processes, like nmh scan(1) or playing music with mpv(1). Second, in the middle, I run something that uses the filesystem a lot, like a borg(1) backup. The first thing's output will stop for a moment while the second thing runs. Best salutations, Ipsen