This is what they call RTFM...in the old 11.2.2.x version, there does not seem to be the word "objective" in the pdf documentation for Exadata Storage Server Software - User's Guide (E13861-05), updated Jan-2010.
In this pdf for 184.108.40.206.1.130109, the word "objective" is key for turning the I/O rationing/prioritization off or on.
I am talking about Exadata Storage Server Software - User's Guide (E13861-14), updated July-2012.
So, you set it to basic and you turn it off.
You set it to balanced or low_latency or high_throughput or auto, you turn it on.
Note to self: RTFM