Completely fair queueing

Completely Fair Queuing, or CFQ, is an I/O scheduler for the Linux kernel that was written in 2003 by Jens Axboe. It places the synchronous requests submitted by processes into a number of per-process queues and then allocates timeslices for each queue to access the disk, with the length of the slice and the number of requests a queue may submit depending on the I/O priority of the process. Asynchronous requests from all processes are batched into fewer queues, one per priority. CFQ lets a process queue idle at the end of synchronous I/O, which has the same effect as anticipatory scheduling. It grew from an idea of Andrea Arcangeli, was merged into mainline kernel 2.6.6 in 2004, became the default scheduler in kernel 2.6.18 in 2006, and was removed in kernel 5.0 in 2019, when it evolved into Budget Fair Queueing.