From: Alex Brainman <alex.brainman@gmail.com>
Date: Mon, 23 Nov 2015 04:26:00 +0000 (+1100)
Subject: runtime: do not call timeBeginPeriod on windows
X-Git-Tag: go1.6beta1~326
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=ab4c9298b8185a056ff1152f2c7bd9b38d3d06f3;p=gostls13.git

runtime: do not call timeBeginPeriod on windows

Calling timeBeginPeriod changes Windows global timer resolution
from 15ms to 1ms. This used to improve Go runtime scheduler
performance, but not anymore. Thanks to @aclements, scheduler now
behaves the same way if we call timeBeginPeriod or not.

Remove call to timeBeginPeriod, since it is machine global
resource, and there are downsides of using low timer resolution.
See issue #8687 for details.

Fixes #8687

Change-Id: Ib7e41aa4a81861b62a900e0e62776c9ef19bfb73
Reviewed-on: https://go-review.googlesource.com/17164
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Yasuhiro MATSUMOTO <mattn.jp@gmail.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
---

diff --git a/src/runtime/export_windows_test.go b/src/runtime/export_windows_test.go
index 703b422ac2..f712c6f653 100644
--- a/src/runtime/export_windows_test.go
+++ b/src/runtime/export_windows_test.go
@@ -8,10 +8,7 @@ package runtime
 
 import "unsafe"
 
-var (
-	TestingWER              = &testingWER
-	TimeBeginPeriodRetValue = &timeBeginPeriodRetValue
-)
+var TestingWER = &testingWER
 
 func NumberOfProcessors() int32 {
 	var info systeminfo
diff --git a/src/runtime/os1_windows.go b/src/runtime/os1_windows.go
index 551705797d..90e03674a4 100644
--- a/src/runtime/os1_windows.go
+++ b/src/runtime/os1_windows.go
@@ -47,7 +47,6 @@ import (
 //go:cgo_import_dynamic runtime._WaitForSingleObject WaitForSingleObject%2 "kernel32.dll"
 //go:cgo_import_dynamic runtime._WriteConsoleW WriteConsoleW%5 "kernel32.dll"
 //go:cgo_import_dynamic runtime._WriteFile WriteFile%5 "kernel32.dll"
-//go:cgo_import_dynamic runtime._timeBeginPeriod timeBeginPeriod%1 "winmm.dll"
 
 var (
 	// Following syscalls are available on every Windows PC.
@@ -90,8 +89,7 @@ var (
 	_WSAGetOverlappedResult,
 	_WaitForSingleObject,
 	_WriteConsoleW,
-	_WriteFile,
-	_timeBeginPeriod stdFunction
+	_WriteFile stdFunction
 
 	// Following syscalls are only available on some Windows PCs.
 	// We will load syscalls, if available, before using them.
@@ -161,8 +159,6 @@ const (
 // in sys_windows_386.s and sys_windows_amd64.s
 func externalthreadhandler()
 
-var timeBeginPeriodRetValue uint32
-
 func osinit() {
 	asmstdcallAddr = unsafe.Pointer(funcPC(asmstdcall))
 
@@ -178,8 +174,6 @@ func osinit() {
 
 	stdcall2(_SetConsoleCtrlHandler, funcPC(ctrlhandler), 1)
 
-	timeBeginPeriodRetValue = uint32(stdcall1(_timeBeginPeriod, 1))
-
 	ncpu = getproccount()
 
 	// Windows dynamic priority boosting assumes that a process has different types
diff --git a/src/runtime/syscall_windows_test.go b/src/runtime/syscall_windows_test.go
index 8b9945b22d..30630bc904 100644
--- a/src/runtime/syscall_windows_test.go
+++ b/src/runtime/syscall_windows_test.go
@@ -642,13 +642,6 @@ uintptr_t cfunc(callback f, uintptr_t n) {
 	}
 }
 
-func TestTimeBeginPeriod(t *testing.T) {
-	const TIMERR_NOERROR = 0
-	if *runtime.TimeBeginPeriodRetValue != TIMERR_NOERROR {
-		t.Fatalf("timeBeginPeriod failed: it returned %d", *runtime.TimeBeginPeriodRetValue)
-	}
-}
-
 // removeOneCPU removes one (any) cpu from affinity mask.
 // It returns new affinity mask.
 func removeOneCPU(mask uintptr) (uintptr, error) {