1. A method for performing an efficient constrained shortest path first (CSPF) optimization of Traffic Engineering (TE) Label Switched Paths (LSPs) in a computer network, the method comprising: detecting a topology change in the computer network that adds or restores a link or a node in the computer network, or a resource change in the computer network that increases available bandwidth on a link in the computer network, that could create a more optimal path for TE-LSPs; selecting a root node for a CSPF computation based on the root node being adjacent to the topology change or resource change, and based on the root node being located along a particular TE-LSP, wherein the root node is located downstream from a head-end node of the particular TE-LSP; and performing the CSPF computation for the particular TE-LSP rooted at the root node; applying a configurable margin to the current cost of the particular TE-LSP prior to determining during the CSPF computation if a higher new cost than a current cost of the particular TE-LSP is reached; determining during the CSPF computation if a higher new cost than the current cost of the particular TE-LSP is reached; and if so stopping the CSPF computation.