Looking at the specfile, here's what realtime-setup gets you:

1. Create a realtime group:
   /usr/sbin/groupadd -f -g 71 realtime
2. Turns on "panic on hung task":
   sysctl -w kernel.hung_task_panic=0 >/dev/null 2>&1
3. Sets "hung task" threshold to 600 seconds:
   sysctl -w kernel.hung_task_timeout_secs=600
4. Installs and enables systemd realtime-setup service file:
   install -m 644 -D realtime-setup.service /usr/lib/systemd/system/realtime-setup.service
   systemctl enable realtime-setup
5. installs realtime rules in /etc/security/limits.d/realtime.conf:
   @realtime       soft    cpu             unlimited
   @realtime       -       rtprio          99
   @realtime       -       nice            -20
   @realtime       -       memlock         unlimited
6. install udev rules in /etc/udev/rules.d/99-rhel-rt.rules
   # udev rules specific to RHEL-RT Realtime kernel
   # insure /dev/rtc points to /dev/rtc0
   # we use PROGRAM rather than SYMLINK because there is
   # a (good) possibility that a /dev/rtc device file
   # already exists and we want to replace it (hence the
   # ln -sf)
   KERNEL=="rtc0", PROGRAM+="/bin/ln -sf rtc0 /dev/rtc"
   # Give permission to the realtime group to write a zero to /dev/cpu_dma_latency
   # This will tell the power management system not to transition to a high cstate
   KERNEL=="cpu_dma_latency", GROUP="realtime"
   # Give permission to the realtime group to read the per cpu msr and cpuid
   # registers. This is needed by cyclictest in rt-tests when using the new
   # feature to read the smi counters. This is necessary but not sufficient
   # A program that wants to access these registers will also need CAP_SYS_RAWIO
   SUBSYSTEM=="msr", GROUP="realtime", MODE="0640"
   SUBSYSTEM=="cpuid", GROUP="realtime", MODE="0640"
7. install sysconfig rules for RT in /etc/sysconfig/realtime-setup
   #
   # Decide whether to turn off SLUB cpu_partial support
   #
   SLUB_CPU_PARTIAL="off"
8. install script to turn off SLUB cpu-partial support:
   /usr/bin/slub_cpu_partial_off
9. install kernel-is-rt script in /usr/sbin/kernel-is-rt
10. install a C binary that enables socket timestamping:
    install -m 755 -D -s realtime-entsk /usr/sbin/realtime-entsk