TDF_SLICEEND
preempted = (td->td_flags & TDF_SLICEEND) == 0 &&
td->td_flags &= ~TDF_SLICEEND;
td->td_flags |= TDF_SLICEEND;
preempted = (td->td_flags & TDF_SLICEEND) == 0 &&
td->td_flags &= ~(TDF_PICKCPU | TDF_SLICEEND);
td->td_flags |= TDF_SLICEEND;