Program Phase Directed Dynamic Cache Way Reconfiguration for Power Efficiency

Aggressive superscalar processor with deep pipeline and sophisticated speculative execution techniques is pushing the power budget to its limit. It is found that a significant portion of this power is wasted during wrong path execution and non power optimal allocation of power hungry resources. Dynamic reconfiguration of micro-architectural resources can be exploited to bring down this waste at runtime. Lack of architectural method to capture the behavior of a program at runtime makes dynamic reconfiguration a challenge. In this paper we propose a method to characterize program behavior at runtime using conflict miss pattern of a data cache, which in turn identifies different program phases in terms of cache utilization. We use this phase information to enable/disable cache ways dynamically depending on the conflict miss pattern of a program. Using a hardware tracking mechanism we ensure that the program performance (throughput in terms of IPC) does not degrade beyond a tolerable limit. Through simulation we establish that an average improvement of 32% (best case 38%) in cache power saving is achieved at the expense of less than 2% degradation in performance for SPEC-CPU and MEDIA benchmarks. The additional hardware that detects and captures the phase information is outside the critical path of the processor and does not contribute to the overall delay.