runtime: use QPC for nanotime and time.now on windows/armgo1.12beta1

The previous implementation of nanotime and time.now used a time source
that was updated on the system clock tick, which has a maximum
resolution of about 1ms. On 386 and amd64, this time source maps to
the system performance counter, so has much higher resolution.
On ARM, use QueryPerformanceCounter() to get a high resolution timestamp.

Updates #26148

Change-Id: I1abc99baf927a95b472ac05020a7788626c71d08
Reviewed-on: https://go-review.googlesource.com/c/154758
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 9 insertions, 4 deletions

diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
index 9b34589874..20fe01c403 100644
--- a/src/runtime/os_windows.go
+++ b/src/runtime/os_windows.go
@@ -198,9 +198,12 @@ func loadOptionalSyscalls() {
 	}
 	_NtWaitForSingleObject = windowsFindfunc(n32, []byte("NtWaitForSingleObject\000"))
 
-	if windowsFindfunc(n32, []byte("wine_get_version\000")) != nil {
-		// running on Wine
-		initWine(k32)
+	underWine := windowsFindfunc(n32, []byte("wine_get_version\000")) != nil
+	if underWine || GOARCH == "arm" {
+		initQPC(k32)
+	}
+	if underWine {
+		initWine()
 	}
 }
 
@@ -357,7 +360,7 @@ func nowQPC() (sec int64, nsec int32, mono int64) {
 	return
 }
 
-func initWine(k32 uintptr) {
+func initQPC(k32 uintptr) {
 	_GetSystemTimeAsFileTime = windowsFindfunc(k32, []byte("GetSystemTimeAsFileTime\000"))
 	if _GetSystemTimeAsFileTime == nil {
 		throw("could not find GetSystemTimeAsFileTime() syscall")
@@ -394,7 +397,9 @@ func initWine(k32 uintptr) {
 	// We have to do it this way (or similar), since multiplying QPC counter by 100 millions overflows
 	// int64 and resulted time will always be invalid.
 	qpcMultiplier = int64(timediv(1000000000, qpcFrequency, nil))
+}
 
+func initWine() {
 	useQPCTime = 1
 }