Process variation is one of the most important factors to be considered in recent microprocessor design, since it negatively affects performance, power, and yield of microprocessors. However, by leveraging process variation, overclocking techniques can improve performance. As microprocessors have substantial clock cycle time margin for yield, there is enough room for performance improvement by overclocking techniques. In this paper, we adopt the F-overclocking technique, which increases clock frequency without changing supply voltage. Our experimental results show that the F-overclocking technique significantly improves performance as well as energy consumption. In addition, the F-overclocking technique is superior to the conventional overclocking technique which increases clock frequency and supply voltage together in the perspective of energy efficiency and reliability, showing similar performance improvement. Furthermore, we propose an adaptive overclocking controller which dynamically applies the F-overclocking technique based on the application characteristics. By adopting our adaptive overclocking controller, we further minimize the reliability loss caused by the F-overclocking technique.

In the early design stage of processors, Dynamic Thermal Management (DTM) schemes should be evaluated to avoid excessively high temperature, while minimizing performance overhead. In this paper, we show that conventional thermal simulations using the fixed ambient temperature may lead to the wrong conclusions in terms of temperature, performance, reliability, and leakage power. Though ambient temperature converges to a steady-state value after hundreds of seconds when we run SPEC CPU2000 benchmark suite, the steady-state ambient temperature is significantly different depending on applications and system configuration. To overcome inaccuracy of conventional thermal simulations, we propose that microarchitectural thermal simulations should exploit application/system-dependent ambient temperature. Our evaluation results reveal that performance, thermal behavior, reliability, and leakage power of the same DTM scheme are different when we use the application/system-dependent ambient temperature instead of the fixed ambient temperature. For accurate simulation results, future microarchitectural thermal researchers are expected to evaluate their proposed DTM schemes based on application/system-dependent ambient temperature.

In the early stage of processor design, Dynamic Thermal Management (DTM) schemes should be evaluated to avoid excessively high temperature, while minimizing performance overhead as small as possible. In this paper, we show that conventional thermal simulations using fixed ambient temperature may lead to wrong conclusion in terms of performance and temperature; though ambient temperature converges to a steady state after hundreds of seconds, the steady state ambient temperature is significantly different depending on applications. To overcome the inaccuracy of conventional thermal simulations, we propose that architectural thermal simulation should exploit application-dependent ambient temperature. Our evaluation results show that the performance of the same DTM scheme is different, when application-dependent ambient temperature (compared to fixed temperature) is used. For accurate simulation, future architectural thermal researchers are expected to evaluate their proposed DTM schemes, reflecting application- dependent ambient temperature.

Recently, 3D integration has been regarded as one of the most promising techniques due to its abilities of reducing global wire lengths and lowering power consumption. However, 3D integrated processors inevitably cause higher power density and lower thermal conductivity, since the closer proximity of heat generating dies makes existing thermal hotspots more severe. Without an efficient cooling method inside the package, 3D integrated processors should suffer severe performance degradation by dynamic thermal management as well as reliability problems. In this paper, we analyze the impact of the liquid cooling on a 3D multi-core processor compared to the conventional air cooling. We also evaluate the leakage power consumption and the lifetime reliability depending on the temperature of each functional unit in the 3D multi-core processor. The simulation results show that the liquid cooling reduces the temperature of the L1 instruction cache (the hottest block in this evaluation) by as much as 45 degrees, resulting in 12.8% leakage reduction, on average, compared to the conventional air cooling. Moreover, the reduced temperature of the L1 instruction cache also improves the reliability of electromigration, stress migration, time-dependent dielectric breakdown, thermal cycling, and negative bias temperature instability significantly.