{HEAD ~ A scheduling processor} assigns {TAIL ~ the work items} to the execution engines for generation of the gather entries 
{ HEAD ~ A scheduling processor } assigns { TAIL ~ the work items } to the execution engines for generation of the gather entries
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH