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How to start jackd with realtime scheduling under Fedora 21?

I amt trying to use Ardour (via the ardour3 package) under Fedora 21. Ardour relies on the Jack Audio Connection Kit (henceforth "jack"), but jack is unable to start with realtime scheduling. When started, jack logs the following:

Cannot use real-time scheduling (RR/20)(1: Operation not permitted)
AcquireSelfRealTime error

And Ardour refuses to create a new session.

I have read through /usr/share/doc/jack-audio-connection-kit/README.Fedora. My user is a member of the "jackuser" and "audio" groups:

$ groups
lars wheel audio mock virt jackuser docker

There are limits set in /etc/security/limits.d/95-jack.conf:

@jackuser - rtprio 99
@jackuser - memlock 4194304

And they are active:

$ ulimit -r
99
$ ulimit -l
4194304

SELinux is enabled, but is running in permissive mode:

# sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   permissive
Mode from config file:          permissive
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Max kernel policy version:      29

I have come across posts from many other people who have experienced the same problem, but no solutions or suggestions other than those already mentioned here (e.g., "make sure your use us a member of the jackuser group"). I'm hoping someone here can shed more light on things.