Real-time Scheduler Regression in RHEL 6.4

Issue

• The RHEL 6.4 scheduler performs worse than RHEL 6.3 for processes at POSIX real-time scheduling class SCHED_FIFO come under heavy scheduling contention.
• Specifically, real-time scheduling contention occurs when there are more real-time processes at the same priority that are runnable than there are CPUs to run them. This can be shown with migrate.c, which by default spawns twice as many POSIX threads as CPUs.