如果你的线程不做I/O，同步等，没有其他的运行，1个线程一个核可以让你获得最好的性能。然而，情况很可能并非如此。添加更多的线程通常会有所帮助，但在某种程度上，它们会导致性能下降。

Not long ago, I was doing performance testing on a 2 quad-core machine running an ASP.NET application on Mono under a pretty decent load. We played with the minimum and maximum number of threads and in the end we found out that for that particular application in that particular configuration the best throughput was somewhere between 36 and 40 threads. Anything outside those boundaries performed worse. Lesson learned? If I were you, I would test with different number of threads until you find the right number for your application.

有一件事是肯定的:4k线程将花费更长的时间。这有很多上下文转换。

一次4000个线程是相当高的。

答案是肯定的，也不是。如果您在每个线程中执行大量阻塞I/O，那么是的，您可以在每个逻辑核心中执行3或4个线程时显示显著的加速。

If you are not doing a lot of blocking things however, then the extra overhead with threading will just make it slower. So use a profiler and see where the bottlenecks are in each possibly parallel piece. If you are doing heavy computations, then more than 1 thread per CPU won't help. If you are doing a lot of memory transfer, it won't help either. If you are doing a lot of I/O though such as for disk access or internet access, then yes multiple threads will help up to a certain extent, or at the least make the application more responsive.

如果你的线程不做I/O，同步等，没有其他的运行，1个线程一个核可以让你获得最好的性能。然而，情况很可能并非如此。添加更多的线程通常会有所帮助，但在某种程度上，它们会导致性能下降。

Not long ago, I was doing performance testing on a 2 quad-core machine running an ASP.NET application on Mono under a pretty decent load. We played with the minimum and maximum number of threads and in the end we found out that for that particular application in that particular configuration the best throughput was somewhere between 36 and 40 threads. Anything outside those boundaries performed worse. Lesson learned? If I were you, I would test with different number of threads until you find the right number for your application.

有一件事是肯定的:4k线程将花费更长的时间。这有很多上下文转换。

大量线程(“线程池”)vs每个核心一个线程的一个例子是在Linux或Windows中实现web服务器。

由于在Linux中套接字是轮询的，因此许多线程可能会增加其中一个线程在正确的时间轮询正确的套接字的可能性——但总体处理成本将非常高。

在Windows中，服务器将使用I/O完成端口(IOCPs)实现，这将使应用程序事件驱动:如果I/O完成，操作系统将启动一个备用线程来处理它。当处理完成时(通常是请求-响应对中的另一个I/O操作)，线程返回IOCP端口(队列)等待下一次完成。

如果没有I/O完成，就没有要做的处理，也没有启动线程。

事实上，微软建议在IOCP实现中每个核不超过一个线程。任何I/O都可以附加到IOCP机制。如果需要，应用程序也可以发布IOCs。

实际性能取决于每个线程的自愿屈服程度。例如，如果线程根本不做I/O，也不使用任何系统服务(即它们100%受cpu限制)，那么每个核1个线程是最优的。如果线程执行任何需要等待的操作，那么您必须试验以确定最佳线程数。4000个线程会导致大量的调度开销，所以这可能也不是最优的。

从计算和内存限制的角度(科学计算)来说，4000个线程会让应用程序运行得非常慢。部分问题是上下文切换的开销非常高，而且很可能是内存位置非常差。

但这也取决于您的体系结构。我听说Niagara处理器应该能够使用某种先进的流水线技术在单核上处理多个线程。但是我没有使用这些处理器的经验。