Costing and Transforming JIT Traces for Adaptive Parallelism

Mr J Magnus Morton, University of Glasgow

Tracing JIT compilation generates units of compilation that are easy to analyse and are known to execute frequently. The AJITPar project aims to investigate whether the information in JIT traces can be used to make better scheduling decisions or perform code transformations to adapt the code for a specific parallel architecture. To achieve this goal, a cost model must be developed to estimate the execution time of an individual trace.
 
This paper presents the design and implementation of a system for ex- tracting JIT trace information from the Pycket JIT compiler. We define four increasingly parametric cost models for Pycket traces. We test the accuracy of these cost models for predicting the cost of individual traces on a set of loop-based micro-benchmarks. We also compare the accuracy of the cost models for predicting whole program execution time over the Pycket benchmark suite. Our preliminary results show the two simplest models provide only limited accuracy. The accuracy of the more com- plex models depends on the choice of parameters; in ongoing work we are systematically exploring the parameter space.