completion-latency · shipping · also clat

Completion latency (fio)

Completion latency in fio is the engine-dependent interval from submission of an I/O unit to observation of its completion.

For asynchronous I/O, observation includes fio reaping the completion; clat is not necessarily time spent only inside a storage device [1]. Pool compatible clat means using their own sample counts; a zero-sample mean does not measure zero latency [2].

Relations

related

submission-latency, latency-storage, queue-depth, iops

Citations

1. fio documentation: interpreting slat, clat and lat; engine-dependent timing boundaries. (accessed 2026-10-13)
2. fio 3.41 source: stat.c, add_ddir_lat_json and add_ddir_status_json; latency sample counts and directional runtime denominators. (accessed 2026-10-13)
3. Hesela: fio summaries, latency sample populations and runtime denominators; synthetic examples. (accessed 2026-10-13)

JSON: /data/terms/completion-latency.json