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Stencil Autotuning with Ordinal Regression: Extended Abstract

The increasing performance of today's computer architecture comes with an unprecedented augment of hardware complexity. Unfortunately this results in difficult-to-tune software and consequentially in a gap between the potential peak performance and the actual performance. Automatic tuning is an emerging approach that assists the programmer in managing this complexity. State-of-the-art autotuners are limited, though: they either require long tuning times, e.g., due to iterative searches, or cannot tackle the complexity of the problem due to the limitation of the supervised machine learning (ML) methodologies used. In particular, traditional ML autotuning approaches exploiting classification algorithms (such as neural networks and support vector machines) face difficulties in capturing all features of large search spaces. We propose a new way of performing automatic tuning based on structural learning: the tuning problem is formulated as a version ranking prediction modeling and solved using ordinal regression. We demonstrate its potential on a well-known autotuning problem: stencil computations. We compare state-of-the-art iterative compilation methods with our ordinal regression approach and analyze the quality of the obtained ranking in terms of Kendall rank correlation coefficients.