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今天我测试了 Linq 和 Plinq 查询的性能影响。因此，我使用了有关msdn How to: Measure PLINQ Query Performance的文章。

void Main()
{
        var source = Enumerable.Range(0, 600000000);
        System.Diagnostics.Stopwatch sw;    

        var queryToMeasure1 = from num in source
                             where num % 3 == 0
                             select Math.Sqrt(num);

        var queryToMeasure2 = from num in source.AsParallel()
                             where num % 3 == 0
                             select Math.Sqrt(num);                          

        long freq = Stopwatch.Frequency;
        Console.WriteLine("Timer frequency in ticks per second = {0}", freq);

        Console.WriteLine("Measuring 1");
        sw = System.Diagnostics.Stopwatch.StartNew();   
        foreach (var n in queryToMeasure1) { }  
        Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds);      

        Console.WriteLine("Measuring 2");
        sw = System.Diagnostics.Stopwatch.StartNew();   
        foreach (var n in queryToMeasure2) { }  
        Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds);

        Console.WriteLine("Measuring 3");
        sw = System.Diagnostics.Stopwatch.StartNew();           
        System.Threading.Tasks.Parallel.ForEach(queryToMeasure1, n => {});          
        Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds);

        Console.WriteLine("Measuring 4");
        sw = System.Diagnostics.Stopwatch.StartNew();           
        System.Threading.Tasks.Parallel.ForEach(queryToMeasure2, n => {});      
        Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds);

        Console.WriteLine("Measuring 5");
        sw = System.Diagnostics.Stopwatch.StartNew();   
        queryToMeasure2.ForAll(n => {});    
        Console.WriteLine("Total ticks: {0} - Elapsed time: {1} ms", sw.ElapsedTicks, sw.ElapsedMilliseconds););
}

测试环境：LinqPad4 on Win7 Enterprise, 64bit, 8GB RAM, I7-2600 (8cores)

我想通了，但无法解释为什么一个核心上的查询（测量 1）比并行查询快。我是否必须添加更多选择代表才能从并行任务中受益？

但现在结果：

1.Run：可枚举范围为60000：

Timer frequency in ticks per second = 3312851
Measuring 1
Total ticks: 3525 - Elapsed time: 1 ms
Measuring 2
Total ticks: 15802 - Elapsed time: 4 ms
Measuring 3
Total ticks: 5940 - Elapsed time: 1 ms
Measuring 4
Total ticks: 26862 - Elapsed time: 8 ms
Measuring 5
Total ticks: 4387 - Elapsed time: 1 ms

2.Run：可枚举范围为600000000：

Timer frequency in ticks per second = 3312851
Measuring 1
Total ticks: 29740243 - Elapsed time: 8977 ms
Measuring 2
Total ticks: 33722438 - Elapsed time: 10179 ms
Measuring 3
Total ticks: 77145502 - Elapsed time: 23286 ms
Measuring 4
Total ticks: 120078284 - Elapsed time: 36246 ms
Measuring 5
Total ticks: 30899585 - Elapsed time: 9327 ms

有趣的事实：在执行测试脚本之前使用垃圾收集器会大大增加测量 4 的时间：

3.运行：可枚举范围为 600000000 和垃圾收集器（来自 LinqPad）：

Timer frequency in ticks per second = 3312851
Measuring 1
Total ticks: 29597830 - Elapsed time: 8934 ms
Measuring 2
Total ticks: 33532083 - Elapsed time: 10121 ms
Measuring 3
Total ticks: 76403692 - Elapsed time: 23062 ms
Measuring 4
Total ticks: 58534548 - Elapsed time: 17668 ms
Measuring 5
Total ticks: 32943622 - Elapsed time: 9944 ms

In conclusion, can I say that method 1 is the most suitable option to perform small select queries and method 5 when the select delegates will increase?

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1 回答 1

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你的计算很便宜。它们甚至不是非并行 LINQ 的良好候选者，因为委托调用可能比计算本身更昂贵。PLINQ 有很多额外的开销，比如启动任务、跨线程同步和复制数据。尝试这个：

bool Where(int i) {
 var sum = 0; 
 for (10000 times) {
  sum += i;
 }
 return i % 3 == 0;
}

并在 where 子句中使用该函数。此功能非常昂贵，因此线程和同步带来的开销将不再主导运行时间。

所以基本上，您正在测量 PLINQ 的最坏情况用例。尝试测量一个有趣的。

于 2012-08-24T10:36:35.283 回答