Multi-level phase analysis for sampling simulation

Extremely long simulation time of architectural simulators has been a major impediment to their wide applicability. To accelerate architectural simulation, prior researchers have proposed representative sampling simulation to trade small loss of accuracy for notable speed improvement. Generally, they use fine-grained phase analysis to select only a small representative portion of program execution intervals for detailed cycle-accurate simulation, while functionally simulating the remaining portion. However, though phase granularity is one of the most important factors to simulation speed, it has not been well investigated and most prior researches explore a fine-grained scheme. This limits their effectiveness in further improving simulation speed with the requirement of increasingly complex architectural designs and new lengthy benchmarks. In this paper, by analyzing the impact of phase granularity on simulation speed, we observe that coarse-grained phases can better capture the overall program characteristics with a less number of phases and the last representative phase could be classified in a very early program position, leading to fewer execution internals being functionally simulated. By contrast, fine-grained phases usually have much shorter execution intervals and thus the overall detailed simulation time could be reduced. Based on the above observation, we design a multi-level sampling simulation technique that combines both fine-grained and coarse-grained phase analysis for sampling simulation. Such a scheme uses fine-grained simulation points to represent only the selected coarse-grained simulation points instead of the entire program execution, thus it could further reduce both the functional and detailed simulation time. Experimental results using SPEC2000 show such a framework is effective: using the SimPoint method as baseline, it can reduce about 90% functional simulation time and about 50% detailed simulation time. It finally achieves a geometric average speedup of 14.04X over SimPoint with comparable accuracy.