Power-Efficient DRAM Speculation

Power-Efficient DRAM Speculation (PEDS) is a power optimization targeted at broadcast-based shared-memory multiprocessor systems that speculatively access DRAM in parallel with the broadcast snoop. Although speculatively accessing DRAM has the potential performance advantage of overlapping DRAM latency with the snoop, it wastes power for memory requests that obtain data from other processors' caches. PEDS takes advantage of information provided by a Region Coherence Array to identify requests that have a high likelihood of obtaining data from another processor's cache, and does not access DRAM speculatively for those requests. By doing so, PEDS eliminates DRAM reads, reduces DRAM power consumption, reduces contention for DRAM resources, and increases the opportunity for DRAM power management. PEDS requires almost no additional hardware in systems that incorporate Region Coherence Arrays. Detailed simulation results show PEDS reduces average DRAM read traffic 28-32%, reduces average DRAM power dissipation 17-22%, and reduces average DRAM energy consumption 16-21%.