On the design of the local variable cache in a hardware translation-based Java Virtual Machine

摘要

Hardware bytecode translation is a technique to improve the performance of the Java Virtual Machine (JVM), especially on the portable devices for which dynamic compilation is infeasible. However, since the translation is done on a single bytecode basis, it is likely to generate frequent memory accesses for local variables which can be a performance bottleneck.In this paper, we propose to add a small register file to the datapath of the hardware-translation based JVM and use it as a local variable cache. We evaluate the effectiveness of the local variable cache against the size of the local variable cache which determines the chip area overhead and the operating speed. We also discuss the mechanisms for the efficient parameter passing and the on-the-fly profiling.With two types of exceptions, a 16-entry local variable cache achieved hit ratios of 60 to 98 %. The first type of exceptions is represented by the FFT, which accesses more than 16 local variables. In this case, on-the-fly profiling was effective. The hit ratio of 16-entry cache for the FFT was increased from 44 to 83 %. The second type of exception is represented by the SAXON XSLT processor for which cold misses were significant. The proposed parameter passing mechanism turned 6.4 to 13.3 % of total accesses from miss to hit to the local variable cache.