Abstract; The CERN LHC provided proton and heavy ion collisions during; its Run 2 operation period from 2015 to 2018. Proton-proton; collisions reached a peak instantaneous luminosity of; 2.1× 1034 cm-2s-1, twice the initial; design value, at √(s)=13 TeV. The CMS experiment; records a subset of the collisions for further processing as part of; its online selection of data for physics analyses, using a two-level; trigger system: the Level-1 trigger, implemented in custom-designed; electronics, and the high-level trigger, a streamlined version of; the offline reconstruction software running on a large computer; farm. This paper presents the performance of the CMS high-level; trigger system during LHC Run 2 for physics objects, such as; leptons, jets, and missing transverse momentum, which meet the broad; needs of the CMS physics program and the challenge of the evolving; LHC and detector conditions. Sophisticated algorithms that were; originally used in offline reconstruction were deployed; online. Highlights include a machine-learning b tagging algorithm; and a reconstruction algorithm for tau leptons that decay; hadronically.
