We use a novel virtualization-based approach for computer architecture performance analysis. We present a case study analyzing a hypothetical hybrid main memory, which consists of a first-level DRAM augmented by a 10-100x slower second-level memory. This architecture is motivated by the recent emergence of lower-cost, higher-density, and lower-power alternative memory technologies. To model such a system, we customize a virtual machine monitor (VMM) with delay-simulation and instrumentation code. Benchmarks representing server, technical computing, and desktop productivity workloads are evaluated in virtual machines (VMs). Relative to baseline all-DRAM systems, these workloads experience widely varying performance degradation when run on hybrid main memory systems which have significant amounts of second-level memory.

The trace cache is a recently proposed solution to achieving high instruction fetch bandwidth by buffering and reusing dynamic instruction traces. This work presents a new block-based trace cache implementation that can achieve higher IPC performance with more efficient storage of traces. Instead of explicitly storing instructions of a trace, pointers to blocks constituting a trace are stored in a much smaller trace table. The block-based trace cache renames fetch addresses at the basic block level and stores aligned blocks in a block cache. Traces are constructed by accessing the replicated block cache using block pointers from the trace table. Performance potential of the blockbased trace cache is quantified and compared with perfect branch prediction and perfect fetch schemes. Comparing to the conventional trace cache, the block-based design can achieve higher IPC, with less impact on cycle time.