On Linux vDSO and clock_gettime sometimes being slow Like the previous post on this somewhat dormant blog, I want to share an oddity I discovered that no search engine could really find for me - even though once I found what the problem was, it turns out I was by no means the first person to discover this. Some system calls that are used extremely frequently in Linux can be speeded up by a mechanism called vDSO: a virtual dynamically linked shared object.