SQLserver WaitType : EXECUTION_PIPE_EVENT_INTERNAL One of our production Microsoft SQL Server 2014 (SP1-CU5) 
 experiencing performance issue so I ran the ShortPeriodWaitStats.sql script from Paul S. Randal, SQLskills.com
and the top WaitType is EXECUTION_PIPE_EVENT_INTERNAL it's 50% of all the WaitTypes !
Someone knows something about it ? any tips to track the core pb ?
According to MSDN, EXECUTION_PIPE_EVENT_INTERNAL :


  Occurs during synchronization between producer and consumer parts of batch execution that are submitted through the connection context. 


The inference here is this is an internal wait type used to denote actions occurring inside the batch execution engine.  Since this is an internal engine wait, the only way you'll be able to accurately diagnose if this is an issue would be to raise it directly with Microsoft.  Alternately, if you are @BobWard or @PaulWhite, you could dig up a Windows Debugger, recreate the issue in a non-production environment, an stop the code in the middle of that wait type.  For the rest of us mere mortals, this deserves a call to Microsoft if you are truly worried about it.