Motivation for Variable Length Intervals and Hierarchical Phase Behavior

Most programs are repetitive, where similar behavior can be seen at different execution times. Proposed algorithms automatically group similar portions of a program´s execution into phases, where the intervals in each phase have homogeneous behavior and similar resource requirements. These prior techniques focus on fixed length intervals (such as a hundred million instructions) to find phase behavior. Fixed length intervals can make a program´s periodic phase behavior difficult to find, because the fixed interval length can be out of sync with the period of the program´s actual phase behavior. In addition, a fixed interval length can only express one level of phase behavior. In this paper, we graphically show that there exists a hierarchy of phase behavior in programs and motivate the need for variable length intervals. We describe the changes applied to SimPoint to support variable length intervals. We finally conclude by providing an initial study into using variable length intervals to guide SimPoint