Load Stall Minimization

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The genesis of the idea for this project was an observation made while performing the analysis of profiles from Java benchmarks being run on a Java virtual machine. We observed a number of instances where there were methods in the top 10-20 of the profile who had 80% or so of their execution attributed to a small number of instructions and that when we viewed those instructions the execution time appeared to be due to load stalls. Drawing from this the first goal in this project is to identify sources of stalls in a selection of Java workloads and try to understand the semantics of the program's behaviour at the point of the stall so we could classify the stalls. The goal is to understand where stalls are happening and try to identify patterns with a view to informing techniques to reduce the stalls. Possible approaches to reducing the stalls fall in two broad families of techniques: 1) instruction scheduling and prefetch insertion to mitigate the stalls and; 2) improve object placement in the garbage collector. While both approaches are possible in combination, the benefit of each and the blended performance is unknown.