Ethereum is going to transition to proof-of-stake, making mining obsolescent. Becoming a miner Ethereum Frontier, like all blockchain technologies uses an incentive-driven model of security. As a special case, when you start up your node from scratch, mining will only start once the DAG is built for the current epoch.
Both geth and ethminer implement automatic DAG generation and maintains two DAGs at a time for smooth epoch transitions. Automatic DAG generation is turned on and off when mining is controlled from the console. It is also turned on by default if geth is launched with the --mine option. Note that clients share a DAG
While not directly answering your query, I think you are trying to get handle on how the DAG changes will affect your hash rate. The DAG just changed to epoch 135 and I saw an immediate hash rate reduction on RX 480 8G cards by 0.35% and a reduction on RX 570 4G cards by 0.41% when mining on