Originally Posted by DoctorOhh
Why they are taking up so much cpu time is immaterial if you want to fix it go to Preferences - Behavior and change Job priority from Normal to Low then restart calibre. This will ensure your computer is responsive to you and the calibre-parallel processes will cede to you when you want to do something other than stare at the computer.
You can also control cpu cores via Preferences - Miscellaneous, but once you change Job priority you should be fine.
Pref->Behavior->Job Priority made no difference - a single secondary calibre-parallel process still ran the CPU at 22-25%, if I set the priority to Below Normal with Windows its also makes no difference. Will it yield if all four cores are at 24.n% usage - dunno, don't care - see next para.
I think I've found the root cause - I had Behaviour->Preferred Output set to EPUB and Preferred Input to RTF, because for my main workflow that's the stage I'm at i.e. I'm doing mainly doing RTF conversions to EPUB.
There's a lot of earlier discussion in this thread around this issue, i.e. which format is used to do the counting - I was left with the impression that the pecking order was EPUB, MOBI, otherwise ?? Given I have an EPUB and an RTF for everything, I thought it was using the EPUBs.
On a whim I pushed EPUB to the top of the Preferred Input order and the slow books become fast books and the fast books became even faster books.
Kiwidude mentioned putting a preferred source format list in the plug-in Configuration similar to the one in Behaviour. I'd settle for a being able to specify a single default format as the one to use to do the count - if its not available then... whatever is easiest for kiwidude.
Have to go, I'm in a bricks & mortar Library using their WiFi, its 18:30, and the real Librarian is rattling keys, and wagging her finger...