As processors seek more resource efficiency, theyincreasingly need to target multiple goals at the same time, such as a level of performance, power consumption, and averageutilization. Robust control solutions cannot come fromheuristic-based controllers or even from formalapproaches that combine multiple single-parameter controllers. Such controllers may end-up working against each other. What is needed is control-theoretical MIMO (multiple input, multiple output) controllers, which actuate on multiple inputsand control multiple outputs in a coordinated manner. In this paper, we use MIMO control-theory techniquesto develop controllers to dynamically tune architectural parameters in processors. To our knowledge, this is the first work in this area. We discuss three ways in which a MIMOcontroller can be used. We develop an example of MIMO controllerand show that it is substantiallymore effective than controllers based on heuristics or builtby combining single-parameter formal controllers. The generalapproach discussed here is likely to be increasingly relevantas future processors become more resource-constrained and adaptive.