Win7 和 Win10 之间的定时器差异
Timers differences between Win7 & Win10
我有一个应用程序，我在其中使用 gettimeofday 的 MinGW 实现在 Win7 上实现 "precise" 计时（~1ms 精度）。它工作正常。
但是，当在Win10上使用相同的代码（甚至是相同的*.exe）时，精度急剧下降到著名的15.6ms精度，这对我来说是不够的。
两个问题：
- 您知道造成这种差异的根源是什么吗？ （它是 OS 配置/"features" 吗？）
- 我该如何解决？或者，更好的是，是否有与 OS 配置无关的精确计时器？
注意：std::chrono::high_resolution_clock 似乎有同样的问题（至少它确实显示了 Win10 上的 15.6 毫秒限制）。
根据 Hans Passant 的评论和我这边的其他测试，这里有一个更合理的答案：
15.6 毫秒（1/64 秒）的限制是 well-known on Windows and is the default behavior. It is possible to lower the limit (e.g. to 1ms, through a call to timeBeginPeriod()) though we are not advise to do so, because this affects the global system timer resolution and the resulting power consumption. For instance, Chrome is notorious for doing this。因此，由于计时器分辨率的全局方面，由于第三方程序，人们可能会在没有明确要求的情况下观察到 1 毫秒的精度。
此外，请注意 std::chrono::high_resolution_clock 而不是 在 windows 上具有有效行为（在 Visual Studio 或 MinGW 上下文中）。所以你不能指望这个接口是一个跨平台的解决方案，15.625ms的限制仍然适用
知道了，我们该如何应对呢？好吧，可以使用 timeBeginPeriod() 来提高一些计时器的精度，但是，同样，我们不建议这样做：使用 QueryPerformanceCounter() (QPC)，这是期待 acquire high-resolution time stamps or measure time intervals according to Microsoft. Note that GPC does count elapsed time (and not CPU cycles) 的原生代码的主要 API。这是一个用法示例：
LARGE_INTEGER StartingTime, EndingTime, ElapsedMicroseconds;
LARGE_INTEGER Frequency;
QueryPerformanceFrequency(&Frequency);
QueryPerformanceCounter(&StartingTime);
// Activity to be timed
QueryPerformanceCounter(&EndingTime);
ElapsedMicroseconds.QuadPart = EndingTime.QuadPart - StartingTime.QuadPart;
//
// We now have the elapsed number of ticks, along with the
// number of ticks-per-second. We use these values
// to convert to the number of elapsed microseconds.
// To guard against loss-of-precision, we convert
// to microseconds *before* dividing by ticks-per-second.
//
ElapsedMicroseconds.QuadPart *= 1000000;
ElapsedMicroseconds.QuadPart /= Frequency.QuadPart;
根据 Microsoft，QPC 也适用于 multicore/multithread 上下文，尽管它可以更少 precise/ambiguous:
When you compare performance counter results that are acquired from different threads, consider values that differ by ± 1 tick to have an ambiguous ordering. If the time stamps are taken from the same thread, this ± 1 tick uncertainty doesn't apply. In this context, the term tick refers to a period of time equal to 1 ÷ (the frequency of the performance counter obtained from QueryPerformanceFrequency).
作为附加资源，MS 还提供了 FAQ on how/why use QPC and an explanation on clock/timing in Windows。
我有一个应用程序，我在其中使用 gettimeofday 的 MinGW 实现在 Win7 上实现 "precise" 计时（~1ms 精度）。它工作正常。
但是，当在Win10上使用相同的代码（甚至是相同的*.exe）时，精度急剧下降到著名的15.6ms精度，这对我来说是不够的。
两个问题： - 您知道造成这种差异的根源是什么吗？ （它是 OS 配置/"features" 吗？） - 我该如何解决？或者，更好的是，是否有与 OS 配置无关的精确计时器？
注意：std::chrono::high_resolution_clock 似乎有同样的问题（至少它确实显示了 Win10 上的 15.6 毫秒限制）。
根据 Hans Passant 的评论和我这边的其他测试，这里有一个更合理的答案：
15.6 毫秒（1/64 秒）的限制是 well-known on Windows and is the default behavior. It is possible to lower the limit (e.g. to 1ms, through a call to timeBeginPeriod()) though we are not advise to do so, because this affects the global system timer resolution and the resulting power consumption. For instance, Chrome is notorious for doing this。因此，由于计时器分辨率的全局方面，由于第三方程序，人们可能会在没有明确要求的情况下观察到 1 毫秒的精度。
此外，请注意 std::chrono::high_resolution_clock 而不是 在 windows 上具有有效行为（在 Visual Studio 或 MinGW 上下文中）。所以你不能指望这个接口是一个跨平台的解决方案，15.625ms的限制仍然适用
知道了，我们该如何应对呢？好吧，可以使用 timeBeginPeriod() 来提高一些计时器的精度，但是，同样，我们不建议这样做：使用 QueryPerformanceCounter() (QPC)，这是期待 acquire high-resolution time stamps or measure time intervals according to Microsoft. Note that GPC does count elapsed time (and not CPU cycles) 的原生代码的主要 API。这是一个用法示例：
LARGE_INTEGER StartingTime, EndingTime, ElapsedMicroseconds;
LARGE_INTEGER Frequency;
QueryPerformanceFrequency(&Frequency);
QueryPerformanceCounter(&StartingTime);
// Activity to be timed
QueryPerformanceCounter(&EndingTime);
ElapsedMicroseconds.QuadPart = EndingTime.QuadPart - StartingTime.QuadPart;
//
// We now have the elapsed number of ticks, along with the
// number of ticks-per-second. We use these values
// to convert to the number of elapsed microseconds.
// To guard against loss-of-precision, we convert
// to microseconds *before* dividing by ticks-per-second.
//
ElapsedMicroseconds.QuadPart *= 1000000;
ElapsedMicroseconds.QuadPart /= Frequency.QuadPart;
根据 Microsoft，QPC 也适用于 multicore/multithread 上下文，尽管它可以更少 precise/ambiguous:
When you compare performance counter results that are acquired from different threads, consider values that differ by ± 1 tick to have an ambiguous ordering. If the time stamps are taken from the same thread, this ± 1 tick uncertainty doesn't apply. In this context, the term tick refers to a period of time equal to 1 ÷ (the frequency of the performance counter obtained from
QueryPerformanceFrequency).
作为附加资源，MS 还提供了 FAQ on how/why use QPC and an explanation on clock/timing in Windows。