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