How to deal with two tasks with the same virtual time

[Parmenides]

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?