This will happen if is greater than or equal to the delay imposed by horizontal constraints, i.e. if If this condition holds, all processors remain active throughout the entire computation, once they have started execution. Or each processor has to wait upon finishing a tile column until the next one is ready. This translates into the condition . In that case, the total computation time is equal to the time at which the last processor starts the execution of the first tile in the last column, namely plus the time needed to process this column. There are tiles per column, and , hence .
Processors remain idle at the end of each tile column, waiting for their next column to be ready.