并行已经线性时间的算法 [英] Parallelize already linear-time algorithm

问题描述

在实践中，有没有一个已经线性时间的算法需要进行并行无论如何？我的老师认为​​，这是不值得，但我不这么认为。

In practice, is there any case that an already linear-time algorithm need to be parallelized? My teacher argue that it is not worth but I don't believe so.

推荐答案

您的老师是错误的。运行时的复杂单CPU的算法（为O（n），O（log n）的，等等）对是否将并行化中获益无关。

Your teacher is mistaken. The run-time complexity (O(n), O(log n), etc.) of the single-CPU algorithm has no bearing on whether or not it will benefit from parallelization.

更改您的code使用1个CPU，以用k处理器将在最好的K的因素划分的运行时间因为你不能随心所欲地创造的CPU凭空，K实际上是一个常数。这样，运行时的复杂性不会受到并行化。所有你能希望做的就是一个常数因子的改善。

Changing your code from using 1 CPU to using K CPUs will at best divide the run time by a factor of K. Since you can't arbitrarily create CPUs out of thin air, K is effectively a constant. So, the run-time complexity is not affected by parallelization. All you can hope to do is get a constant factor improvement.

这并不是说这是不值得做的 - 在某些情况下，两方面的改进是非常有益的。此外，在大规模并行十万CPU的系统中，不断得到pretty的大。

Which isn't to say that it's not worth doing - in some cases, a two-fold improvement is hugely beneficial. Plus, in a massively parallel system of thousands of CPUs, that constant gets pretty big.

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