FIFOa

FIFOa, short for First-In-First-Out with aging, is a queue management discipline used in computing to order the processing of items such as tasks, packets, or I/O requests. It extends classic FIFO by applying a time-dependent aging function that increases the priority of waiting items. The result is a fairer system that can reduce starvation while preserving many of the simplicity benefits of FIFO.

Operation: Each item has a base priority tied to its arrival. Over time, its effective priority increases according to an aging function, for example proportional to its wait time. When selecting the next item to service, the scheduler chooses the item with the highest effective priority. Implementation may recompute priorities on demand or periodically reorder the queue.

Applications: FIFOa appears in operating systems for CPU scheduling, in network devices for packet transmission, and in storage or I/O subsystems for request handling. It is valued for balancing predictability with fairness and can be tuned with aging rate parameters to fit workload patterns.

Variants and considerations: Common aging schemes include linear aging, where priority grows linearly with wait time, and exponential aging, where growth accelerates with delay. Trade-offs include potential increases in average latency for short tasks and added scheduling overhead. Proper tuning is required to avoid excessive reordering or throughput loss in high-load environments.

See also: First-In-First-Out, priority queue, aging, fair queuing.