在此示例中，为什么并行版本比顺序版本慢? [英] Why was the parallel version slower than the sequential version in this example?

问题描述

最近几天我一直在学习有关并行性的知识，并且遇到了

I've been learning a little about parallelism in the last few days, and I came across this example.

我将它与顺序for循环并排放置:

I put it side to side with a sequential for loop like this:

private static void NoParallelTest()
{
    int[] nums = Enumerable.Range(0, 1000000).ToArray();
    long total = 0;
    var watch = Stopwatch.StartNew();
    for (int i = 0; i < nums.Length; i++)
    {
        total += nums[i];
    }
    Console.WriteLine("NoParallel");
    Console.WriteLine(watch.ElapsedMilliseconds);
    Console.WriteLine("The total is {0}", total);
}

我很惊讶地看到NoParallel方法比现场给出的并行示例快得多.

I was surprised to see that the NoParallel method finished way way faster than the parallel example given at the site.

我有一台i5电脑.

我真的以为Parallel方法可以更快地完成.

I really thought that the Parallel method would finish faster.

对此有合理的解释吗?也许我误会了什么?

Is there a reasonable explanation for this? Maybe I misunderstood something?

推荐答案

顺序版本速度更快，因为在示例中对每个迭代进行操作所花费的时间非常小，并且创建和管理多个对象需要相当大的开销线程.

The sequential version was faster because the time spent doing operations on each iteration in your example is very small and there is a fairly significant overhead involved with creating and managing multiple threads.

只有在每次迭代的处理器时间都足够昂贵时，并行编程才能提高效率.

Parallel programming only increases efficiency when each iteration is sufficiently expensive in terms of processor time.

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