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runtime: use CreateWaitableTimerEx to implement usleep
@jstarks suggested that recent versions of Windows provide access to high resolution timers. See #8687 (comment) for details. I tried to run this C program on my Windows 10 computer ``` #include <stdio.h> #include <Windows.h> #pragma comment(lib, "Winmm.lib") // Apparently this is already defined when I use msvc cl. //#define CREATE_WAITABLE_TIMER_HIGH_RESOLUTION = 0x00000002; int usleep(HANDLE timer, LONGLONG d) { LARGE_INTEGER liDueTime; DWORD ret; LARGE_INTEGER StartingTime, EndingTime, ElapsedMicroseconds; LARGE_INTEGER Frequency; QueryPerformanceFrequency(&Frequency); QueryPerformanceCounter(&StartingTime); liDueTime.QuadPart = d; liDueTime.QuadPart = liDueTime.QuadPart * 10; // us into 100 of ns units liDueTime.QuadPart = -liDueTime.QuadPart; // negative for relative dure time if (!SetWaitableTimer(timer, &liDueTime, 0, NULL, NULL, 0)) { printf("SetWaitableTimer failed: errno=%d\n", GetLastError()); return 1; } ret = WaitForSingleObject(timer, INFINITE); if (ret != WAIT_OBJECT_0) { printf("WaitForSingleObject failed: ret=%d errno=%d\n", ret, GetLastError()); return 1; } QueryPerformanceCounter(&EndingTime); ElapsedMicroseconds.QuadPart = EndingTime.QuadPart - StartingTime.QuadPart; ElapsedMicroseconds.QuadPart *= 1000000; ElapsedMicroseconds.QuadPart /= Frequency.QuadPart; printf("delay is %lld us - slept for %lld us\n", d, ElapsedMicroseconds.QuadPart); return 0; } int testTimer(DWORD createFlag) { HANDLE timer; timer = CreateWaitableTimerEx(NULL, NULL, createFlag, TIMER_ALL_ACCESS); if (timer == NULL) { printf("CreateWaitableTimerEx failed: errno=%d\n", GetLastError()); return 1; } usleep(timer, 1000LL); usleep(timer, 100LL); usleep(timer, 10LL); usleep(timer, 1LL); CloseHandle(timer); return 0; } int main() { printf("\n1. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is off - timeBeginPeriod is off\n"); testTimer(0); printf("\n2. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is on - timeBeginPeriod is off\n"); testTimer(CREATE_WAITABLE_TIMER_HIGH_RESOLUTION); timeBeginPeriod(1); printf("\n3. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is off - timeBeginPeriod is on\n"); testTimer(0); printf("\n4. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is on - timeBeginPeriod is on\n"); testTimer(CREATE_WAITABLE_TIMER_HIGH_RESOLUTION); } ``` and I see this output ``` 1. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is off - timeBeginPeriod is off delay is 1000 us - slept for 4045 us delay is 100 us - slept for 3915 us delay is 10 us - slept for 3291 us delay is 1 us - slept for 2234 us 2. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is on - timeBeginPeriod is off delay is 1000 us - slept for 1076 us delay is 100 us - slept for 569 us delay is 10 us - slept for 585 us delay is 1 us - slept for 17 us 3. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is off - timeBeginPeriod is on delay is 1000 us - slept for 742 us delay is 100 us - slept for 893 us delay is 10 us - slept for 414 us delay is 1 us - slept for 920 us 4. CREATE_WAITABLE_TIMER_HIGH_RESOLUTION is on - timeBeginPeriod is on delay is 1000 us - slept for 1466 us delay is 100 us - slept for 559 us delay is 10 us - slept for 535 us delay is 1 us - slept for 5 us ``` That shows, that indeed using CREATE_WAITABLE_TIMER_HIGH_RESOLUTION will provide sleeps as low as about 500 microseconds, while our current approach provides about 1 millisecond sleep. New approach also does not require for timeBeginPeriod to be on, so this change solves long standing problem with go programs draining laptop battery, because it calls timeBeginPeriod. This change will only run on systems where CREATE_WAITABLE_TIMER_HIGH_RESOLUTION flag is available. If not available, the runtime will fallback to original code that uses timeBeginPeriod. This is how this change affects benchmark reported in issue #14790 name old time/op new time/op delta ChanToSyscallPing 1.05ms ± 2% 0.68ms ±11% -35.43% (p=0.000 n=10+10) The benchmark was run with GOMAXPROCS set to 1. Fixes #8687 Updates #14790 Change-Id: I5b97ba58289c088c17c05292e12e45285c467eae Reviewed-on: https://go-review.googlesource.com/c/go/+/248699 Run-TryBot: Alex Brainman <alex.brainman@gmail.com> TryBot-Result: Go Bot <gobot@golang.org> Trust: Alex Brainman <alex.brainman@gmail.com> Reviewed-by: Austin Clements <austin@google.com>
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