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====== Scheduling - RT throttling ======

Programming failures in real-time applications can cause the entire system to hang. Such a failure could act like a call of a `while(true){}` loop. When the real-time application has the highest possible priority and is scheduled with SCHED_FIFO policy, no other task can preempt it. This leads to the system blocking all other tasks and scheduling this loop with a CPU load of 100 percent. Real-time throttling is a mechanism to avoid such situations by limiting the execution time of real-time tasks per period. The settings are exported into the proc file system. The default settings are:

  # cat /proc/sys/kernel/sched_rt_period_us
  1000000
  # cat /proc/sys/kernel/sched_rt_runtime_us
  950000

To reach a only 50% CPU usage for real-time tasks and a larger period the values can be changed with the following commands:

  # echo 2000000 > /proc/sys/kernel/sched_rt_period_us
  # echo 1000000 > /proc/sys/kernel/sched_rt_runtime_us

Real-time throttling is disabled in case the real-time task runtime has the same length than the the period. This is done automatically by writing `-1` into `sched_rt_runtime_us`:

  # echo -1 > /proc/sys/kernel/sched_rt_runtime_us

This mechanism is already implemented in mainline Linux.

References:
  * [[https://docs.kernel.org/scheduler/sched-deadline.html|Deadline Task Scheduling]]
  * [[https://docs.kernel.org/scheduler/sched-rt-group.html|Real-Time group scheduling]]
  * [[https://docs.kernel.org/scheduler/sched-bwc.html|CFS Bandwidth Control]]
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