Tracing JIT compilation generates units of compilation that are easy to analyse and are known to execute frequently. The AJITPar project investigates whether the information in JIT traces can be used to dynamically transform programs for a specific parallel architecture. Hence a lightweight cost model is required for JIT traces. This paper presents the design and implementation of a system for extracting JIT trace information from the Pycket JIT compiler. We define three increasingly parametric

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... cost models for Pycket traces. We determine the best weights for the cost model parameters using linear regression. We evaluate the effectiveness of the cost models for predicting the relative costs of transformed programs.