For Run III (2021 onwards) of the LHC, LHCb will take data at an instantaneous
luminosity of $2 \times 10^{33} \mathrm{cm}^{-2} \mathrm{s}^{-1}$, five times
higher than in Run II (2015-2018). To cope with the harsher data taking
conditions, the LHCb collaboration will upgrade the DAQ system and install a
purely software based trigger, in addition to various detector upgrades. The
high readout rate contributes to the challenge of reconstructing and selecting
events in real time.

Special emphasis in this contribution will be put on the need for fast track
reconstruction in the software trigger. The modified detector
infrastructure will be able to face this challenge and the necessary
changes to the reconstruction sequence are discussed. A novel strategy is presented which
distributes and maximises the bandwidth among the different physics channels
using a genetic algorithm.

The data processing chain includes a redesign of the event scheduling,
introduction of concurrent processing, optimisations in processor cache
accesses and code vectorisation. Furthermore changes in the areas of event
model, conditions data and detector description are foreseen.