  The CMS experiment has been designed with a two-level trigger system: the
Level-1 Trigger, implemented on custom-designed electronics, and the High Level
Trigger, a streamlined version of the CMS offline reconstruction software
running on a computer farm. During its second phase the LHC will reach a
luminosity of $7.5\times10^{34}\,\textrm{cm}^{-2}\,\textrm{s}^{-1}$ with a
pileup of 200 collisions, producing integrated luminosity greater than 3000
fb$^{-1}$ over the full experimental run. To fully exploit the higher
luminosity, the CMS experiment will introduce a more advanced Level-1 Trigger
and increase the full readout rate from 100 kHz to 750 kHz. CMS is designing an
efficient data-processing hardware trigger (Level-1) that will include tracking
information and high-granularity calorimeter information. The current
conceptual system design is expected to take full advantage of advances in FPGA
and link technologies over the coming years, providing a high-performance,
low-latency system for large throughput and sophisticated data correlation
across diverse sources. The higher luminosity, event complexity and input rate
present an unprecedented challenge to the High Level Trigger, that aims to
achieve a similar efficiency and rejection factor as today despite the higher
pileup and more pure preselection. In this presentation we will discuss the
ongoing studies and prospects for the online reconstruction and selection
algorithms for the high-luminosity era.
