Multicore/Manycore Parallel Traversal of Large Forests of Regression Trees

Machine-learnt models based on additive ensembles of binary regression trees are currently considered one of the best solutions to address complex classification, regression, and ranking tasks. To evaluate these complex models over a continuous stream of data items with high throughput requirements, we need to optimize, and possibly parallelize, the traversal of thousands of trees, each including hundreds of nodes.Document ranking in Web Search is a typical example of this challenging scenario, where complex tree-based models are used to score query-document pairs and finally rank lists of document results for each incoming query (a.k.a. Learning-to-Rank). In this extended abstract, we briefly discuss some preliminary results concerning the parallelization strategies for QUICKSCORER – indeed the state-of-art scoring algorithm that exploits ensembles of decision trees – by using multicore CPUs (with SIMD coprocessors) and manycore GPUs. We show that QUICKSCORER, which transforms the traversal of thousands of decision trees in a linear access to array data structures, can be parallelized very effectively, by achieving very interesting speedups.