一种改进的TreePM码
A Modified TreePM Code
摘要：
我们讨论的性能特点，使用巴恩斯\citep{1990JCoPh..87..161B}的上下文中的TreePM代码的树代码的修改建议。优化涉及识别粒子组，并仅使用一次树行走来计算组中所有粒子的力。这种修改已经在我们的TreePM代码实现中使用了一段时间，并且也被其他人用于使用树结构的代码中。在本文中，我们提出了这种优化的性能特点的第一个详细的研究。我们表明，修改，如果调整得当，可以加快TreePM代码的显着金额。我们还结合使用单独的时间步长，并指出如何结合这两个计划在一个最佳的方式修改。我们发现，该组合至少比没有单独时间步长的修改后的TreePM快两倍。总体性能通常会更快，因为组方案优化了大型模拟的缓存使用。
英文摘要：
We discuss the performance characteristics of using the modification of the tree code suggested by Barnes \citep{1990JCoPh..87..161B} in the context of the TreePM code. The optimisation involves identifying groups of particles and using only one tree walk to compute force for all the particles in the group. This modification has been in use in our implementation of the TreePM code for some time, and has also been used by others in codes that make use of tree structures. In this paper, we present the first detailed study of the performance characteristics of this optimisation. We show that the modification, if tuned properly can speed up the TreePM code by a significant amount. We also combine this modification with the use of individual time steps and indicate how to combine these two schemes in an optimal fashion. We find that the combination is at least a factor of two faster than the modified TreePM without individual time steps. Overall performance is often faster by a larger factor, as the scheme of groups optimises use of cache for large simulations.
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