Comparing program phase detection techniques

Detecting program phase changes accurately is an important aspect of dynamically adaptable systems. Three dynamic program phase detection techniques are compared - using instruction working sets, basic block vectors (BBV), and conditional branch counts. Because program phases are difficult to define, we compare the techniques using a variety of metrics. BBV techniques perform better than the other techniques providing higher sensitivity and more stable phases. However, the instruction working set technique yields 30% longer phases than the BBV method, although there is less stability within phases. On average, the methods agree on phase changes 85% of the time. Of the 15% of time they disagree, the BBV method is more efficient at detecting performance changes. The conditional branch counter technique provides good sensitivity, but is less effective at detecting major phase changes. Nevertheless, the branch counter technique correlates 83% of the time with the BBV based technique. As an auxiliary result, we show that techniques based on procedure granularities do not perform as well as those based on instruction or basic block granularities. This is mainly due to their inability to detect changes within procedures.