Completely Fair Scheduler

CFS is a multilevel queue scheduling but using Cgroups in place of multiple queues.

Operating System will save how much time a process has consumed. A process that has high priority and high access, scheduler will reduce the access after some time.

• Fair
• Proportional share scheduling
• Virtual runtime (vruntime)
  • Take into account how much time the process has accessed the CPU. After some time, it will reduce their access.
• Red-Black trees (self-balancing binary search tree) to implement vruntime
• Time slices and preemption
  • Time assigned to processes is not the same. Time slices can be different and after Linux gets back the time.
• Load balancing
  • Processes are dynamically assigned to different cores. Put unused cores on hold to not use battery.
• Tuning with nice values.
  • Indicate if a process is important or not as a user.
  • Use nice to first run a process with a priority -20 to 20.
  • renice used for programs already running.
  • Super user (root user) can give any value to renice. Other users can only reduce priority.