How to deal with two tasks with the same virtual time

Hi, As far as the CFS scheduler is concerned, every task, whose key is the task's virtual time, will be inserted into a red-black tree to improve the performence of seaching specified task. But, that works well only if any task's vritual time is different with the others tasks'. So, I wonder whether there are chances that two tasks occasionally have the same virtual time. If so, how to deal with it?