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