  The CMS experiment has been designed with a 2-level trigger system: the Level
1 Trigger, implemented on custom-designed electronics, and the High Level
Trigger (HLT), a streamlined version of the CMS offline reconstruction software
running on a computer farm. A software trigger system requires a tradeoff
between the complexity of the algorithms running on the available computing
power, the sustainable output rate, and the selection efficiency. Here we will
present the performance of the main triggers used during the 2012 data taking,
ranging from simpler single-object selections to more complex algorithms
combining different objects, and applying analysis-level reconstruction and
selection. We will discuss the optimisation of the triggers and the specific
techniques to cope with the increasing LHC pile-up, reducing its impact on the
physics performance.
