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