Yesterday was the first time I've ever used real-time priority for real...
Our old computer died a couple of days previously, and one of the things hanging off it was a scanner. So I moved it to the main server, but encountered the problem that it really doesn't like being slowed down. That didn't matter much on the old computer, because that's the only thing it was doing, but on the server there's all kinds of background (and foreground) things going on; it didn't have a chance.
With (soft) real-time priority, it works.
chrt -r 1 timeout 600 scanimage -d canon_pp ...
By the way, chrt is a Czech word (pronounced [xr̩t]) meaning greyhound, but I assume that's just a coincidence.
The downside is that it's largely CPU-bound; it lets up a bit every second or so, but the computer is largely stopped while a scan is going on. I have no idea how it manages to be CPU-bound, but it is - probably a busy-wait somewhere there shouldn't be one.
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