ALICE FIT data processing and performance during LHC Run 3

During the upcoming Run 3 and Run 4 at the LHC the upgraded ALICE (A Large Ion Collider Experiment) will operate at a significantly higher luminosity and will collect two orders of magnitude more events than in Run 1 and Run 2. A part of the ALICE upgrade is the new Fast Interaction Trigger (FIT). This thoroughly redesigned detector combines, in one system, the functionality of the four forward detectors used by ALICE during the LHC Run 2: T0, V0, FMD, and AD. The FIT will monitor luminosity and background, provide feedback to the LHC, and generate minimum bias, vertex and centrality triggers, in real time. During the offline analysis FIT data will be used to extract the precise collision time needed for time-of-flight (TOF) particle identification. During the heavy-ion collisions, FIT will also determine multiplicity, centrality, and event plane. The FIT electronics is designed to function both in the continuous and the triggered readout mode. In these proceedings the FIT simulation, software, and raw data processing are briefly described. However, the main focus is on the detector performance, trigger efficiencies, collision time, and centrality resolution.