Thermal Sensors and Adaptivity for Power Reduction

1. Accessed frequently Gate Put in Drowsy Line brought into cache 35οC Accessed frequently Put in Drowsy Gate Line brought into cache 85οC Static Power Saved over stationary approach ~24% Cache Line Idle 65οC 45οC 35οC Hybrid 85οC Drowsy 110οC Thermal Sensors and Adaptivity for Power Reduction HiPeac Summer School 2005 APEL: Applied Electronics Laboratory University of Patras, Patras Greece Polychronis Xekalakis, Stefanos Kaxiras, Georgios Keramidas xekalakis@apel.ee.upatras.gr, kaxiras,keramidas@ee.upatras.gr Key Ideas Use 4T Dram Cells as Thermal Sensors Adapt Hybrid Decay-Drowsy Scheme in Accordance to Temperature 3. Thermally Adaptive Hybrid Drowsy-Decay Scheme 1. 4T Dram Decay Sensors How it Works A day of a Cache Line in a Hybrid Thermally Adaptive Scheme • Initially 4T Cell is Charged • When it loses it’s charge generates a pulse and resets charge of the cell • Rate at which loses charge proportional to leakage currents • Leakage currents proportional to temperature • Frequency of pulses proportional to temperature • Cache Line brought into cache and frequently accessed • Cache Line Idle: • Put line in Drowsy state • Gate the cache line • Drowsy kept Constant with temperature (little variation) • Decay varies with Temperature (use 4T cell) Sensors Characteristic Effect of Process Variation Stationary Hybrid and Drowsy Normalized Energy Savings vs. Temperature The Mechanics 2. Leakage Techniques that Adapt to Temperature Why we Need Them • Gate Leakage exponentially depends on Temperature • Temperature Changes with program execution • All leakage saving techniques try to minimize dynamic to static ratio • Stationary approach sub-optimal and this worsens as technology scales • Gate Leakage is and will be dominant Leakage Current Normalized Energy Savings vs. Temperature Perfect Temperature Adaptivity Ideal Hybrid 4T Hybrid Decay Drowsy Hybrid Leakage Current: Moore’s Law Meets Static Power Nam Sung Kim, Todd Austin, David Blaauw, Trevor Mudge