Naïve Parallelism: a rebuttal

Several people including Simon Marlow of Microsoft have objected to our rejection of Saynte's new Haskell code, claiming that the alterations were minor and that they optimize serial performance. This is simply not true. Firstly, over half of the lines of code in the entire program have been altered. Secondly, the new version is slower than Lennart's original version 5 on 1 core. So there is no logical reason to choose the revised Haskell for the basis of a naive parallelization unless you want to cherry pick results by leveraging knowledge of how they will scale after parallelization. Suffice to say, doing so would be bad science.

This is illustrated in the following graph of performance results for Lennart's original version 5 vs Saynte's new revised Haskell with 11 levels of spheres at 1,024×1,024:

The original code is 5% faster on 1 core but scales poorly and is 2.7× slower on 7 cores. The substantially-revised "serial" Haskell code was obviously specifically designed to be amenable to parallelization and, therefore, had no place in a comparison about naive parallelizations.

This naturally raises the question of how the different programs will perform when optimized for parallelism. A fair comparison will require the C++ to be rewritten just as the revised Haskell had been. We shall address this question in the future.

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