The two tracepoints are used to delimit the beginning and the end of the
execution of a task by a scheduler.  The beginning tracepoint contains all the
meta information related to the the execution context of the task and an unique
cookie.  This cookie is then reused in the end tracepoint to match the pair of
begin/end without duplication of information.

Change-Id: Ibbf64fe49325e7cb72c60aa6c9d8d8d1ab074f2a