CGEventPost在图形处理器负载下的弱性能
我们偶然发现了一个与Quartz事件有关的性能问题，更具体地说是CGEventPost:在繁重的GPU负载期间，GPU可能会阻塞。我们创建了a small benchmark application to demonstrate the issue。这个应用程序只是一个创建、发布和释放事件的循环。
下面您可以看到运行应用程序的结果。第一次运行是在空闲系统上。第二次运行是使用FurMark (图形处理器压力测试)，尽可能调高刻度盘。
- 内部是内部循环需要多长时间，基本上只是创建、发布和释放一个带有Quartz事件的事件。
- 外部是我们的程序等待被唤醒(睡眠)的时间。应该接近我们的睡眠时间，但如果系统有压力，它可能会被延迟。
- 帖子是事件帖子所需的时间。
18:58:01.683 EventPerformance[4946:707] Measurements: (outer should be close to 10)
18:58:01.684 EventPerformance[4946:707] inner (ms): 0.04, outer (ms): 11.02, CGEventPost (ms): 0.03
18:58:01.684 EventPerformance[4946:707] inner (ms): 0.04, outer (ms): 11.02, CGEventPost (ms): 0.03
18:58:01.685 EventPerformance[4946:707] inner (ms): 0.07, outer (ms): 10.26, CGEventPost (ms): 0.03
18:58:01.685 EventPerformance[4946:707] inner (ms): 0.06, outer (ms): 10.85, CGEventPost (ms): 0.05
18:58:01.686 EventPerformance[4946:707] inner (ms): 0.07, outer (ms): 10.41, CGEventPost (ms): 0.04
18:58:01.686 EventPerformance[4946:707] inner (ms): 0.04, outer (ms): 10.39, CGEventPost (ms): 0.03
18:58:01.686 EventPerformance[4946:707] inner (ms): 0.05, outer (ms): 11.02, CGEventPost (ms): 0.03
18:58:01.687 EventPerformance[4946:707] inner (ms): 0.03, outer (ms): 10.67, CGEventPost (ms): 0.03
18:58:01.687 EventPerformance[4946:707] inner (ms): 0.08, outer (ms): 10.09, CGEventPost (ms): 0.05
18:58:01.688 EventPerformance[4946:707] Averages: (outer should be close to 10)
18:58:01.688 EventPerformance[4946:707] avg inner (ms): 0.05, avg outer (ms): 10.64, avg post (ms): 0.03在这里我们可以看到，发布事件平均需要0.03毫秒。此外，线程似乎在0.5ms左右被唤醒得太晚了。CGEventPost中没有尖峰。
19:02:02.150 EventPerformance[5241:707] Measurements: (outer should be close to 10)
19:02:02.151 EventPerformance[5241:707] inner (ms): 0.03, outer (ms): 10.23, CGEventPost (ms): 0.02
19:02:02.151 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 10.54, CGEventPost (ms): 0.02
19:02:02.151 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 11.01, CGEventPost (ms): 0.01
19:02:02.152 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 10.74, CGEventPost (ms): 0.01
19:02:02.152 EventPerformance[5241:707] inner (ms): 0.02, outer (ms): 10.20, CGEventPost (ms): 0.01
19:02:02.152 EventPerformance[5241:707] inner (ms): 10.35, outer (ms): 11.01, CGEventPost (ms): 10.35
19:02:02.152 EventPerformance[5241:707] inner (ms): 0.03, outer (ms): 10.02, CGEventPost (ms): 0.02
19:02:02.153 EventPerformance[5241:707] inner (ms): 58.90, outer (ms): 10.11, CGEventPost (ms): 58.90
19:02:02.153 EventPerformance[5241:707] inner (ms): 0.03, outer (ms): 10.12, CGEventPost (ms): 0.02
19:02:02.153 EventPerformance[5241:707] Averages: (outer should be close to 10)
19:02:02.371 EventPerformance[5241:707] avg inner (ms): 7.71, avg outer (ms): 10.44, avg post (ms): 7.71当系统在繁重的GPU负载下时，发布事件可能需要(峰值)毫秒，而不是微秒。在极端GPU压力(< 1 FPS)下，该值可能需要几秒钟。CGEventPost有时似乎在等待图形处理器完成一些工作后才会返回。我们的线程仍然被正常调度，没有明显的延迟/尖峰(外部)。
任何想法都是值得感谢的。
回答 1
Stack Overflow用户
发布于 2013-03-20 07:16:34
我猜你正在填满队列(底层的mach端口)...
您可以使用Instruments中的"scheduling“或"system call”工具确认这一点。(创建一个新的空白文档，添加仪器，然后在File > Record Options...下确保选中了"deferred“。)这将显示应用程序中的所有线程活动(线程何时阻塞，何时休眠，何时激活，以及原因)。
我会首先尝试提高线程优先级(参见。调用CGEventPost的线程的man 3 PTHREAD_SCHEDPARAM)。如果你的线程在较低优先级的线程上被阻塞，内核应该临时提高阻塞线程的优先级，以避免优先级反转，并帮助你的任务更早完成。
总的来说，我认为您必须实现一个双线程解决方案，如下所示：
为要发布的事件创建一个队列。从您的主线程(或事件发布线程)向此队列发布事件，然后通知第二个线程(您创建的事件使用者线程)遍历队列并使用CGEventPost发布任何未完成的事件。
当CGEventPost阻塞时，您的第二个事件发布线程将阻塞，但这不会阻塞任何其他线程。当CGEventPost最终解除阻塞时，它将使用您的事件消费者线程发布的任何未完成的事件，并且事件消费者线程可以恢复发布事件。
另一种可能性:你能联合事件吗？有一些特定类型的事件(鼠标移动？)你可以合并成更少的事件。您可能有时仍然会遇到CGEventPost的队列限制，我认为双线程方法可能是您最好的选择。
https://stackoverflow.com/questions/14342444
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