Analyzing Fair Share Fairness of Tasks in the Linux Completely Fair Scheduler Using eBPF

The Linux Completely Fair Scheduler (CFS) was designed by the means of allocating CPU resources appropriately based on a certain notion of fairness. Fairness in the context of Completely Fair Scheduler refers to the proportion of CPU time (fair share) each thread/process (task) can use based on its priority level. However, most of the time the actual fair shares that each task receives are different compared to the fair shares dictated by the priority levels, which might lead to unwanted system behaviors. We present a system to monitor the Completely Fair Scheduler - Durian - that utilizes eBPF (extended Berkeley Packet Filter) to emit certain scheduling events and data toward user space which among many things will analyze the actual fairness of fair shares each task gets based on scheduling data and statistics. The system provided, although uses a certain amount of time and resources, will have little to no hindrance to the Linux scheduling algorithm in terms of time and safety.