Description of problem: localhost:~# date ; time systemctl start pmcd.service ; date ; Wed Dec 16 11:23:21 EET 2015 systemctl start pmcd.service 0.00s user 0.01s system 2% cpu 0.457 total Wed Dec 16 11:23:22 EET 2015 localhost:~# date ; time systemctl stop pmcd.service ; date ; Wed Dec 16 11:23:25 EET 2015 systemctl stop pmcd.service 0.01s user 0.01s system 0% cpu 3.349 total Wed Dec 16 11:23:29 EET 2015 localhost:~# While 4 seconds might not sound like "a long time" it's actually more than half of the time spent when shutting down all the services running on a default Fedora installation. IOW, after "poweroff" on Fedora the time to shutdown the system without pmcd is ~1-2 seconds. With pmcd in play the time is ~5-6 seconds.
There are two parts to the problem here, Marko. The first aspect is pmcd itself taking quite a long time to shutdown, due to the way it waits on PMDAs at termination time. Lukas and I ended up tackling this recently, in another context (some pmdaroot(1) work). The second aspect is some overly-long delays in the rc script - I've got a fix and have been testing these (there's sporadic QA fallout), so it might make it for pcp-3.11.0, might not (certainly 3.11.1 otherwise).
This was all tackled in pcp-3.11.0