When the processor is suspended, then the DMA module transfer one word and return control to the processor.

Note that, this is not an interrupt, the processor does not save a context and do something else. Rather, the processor pauses for one bus cycle.

During that time processor may perform some other task which does not involve the system bus. In the worst situation processor will wait for some time, till the DMA releases the bus.

The net effect is that the processor will go slow. But the net effect is the enhancement of performance, because for a multiple word I/O transfer, DMA is far more efficient than interrupt driven or programmed I/O.