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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
// Implement TimeStamp::Now() with QueryPerformanceCounter() controlled with
// values of GetTickCount64().
#include "mozilla/DynamicallyLinkedFunctionPtr.h"
#include "mozilla/MathAlgorithms.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/Uptime.h"
#include <stdio.h>
#include <stdlib.h>
#include <intrin.h>
#include <windows.h>
// To enable logging define to your favorite logging API
#define LOG(x)
class AutoCriticalSection {
public:
explicit AutoCriticalSection(LPCRITICAL_SECTION aSection)
: mSection(aSection) {
::EnterCriticalSection(mSection);
}
~AutoCriticalSection() { ::LeaveCriticalSection(mSection); }
private:
LPCRITICAL_SECTION mSection;
};
// Estimate of the smallest duration of time we can measure.
static volatile ULONGLONG sResolution;
static volatile ULONGLONG sResolutionSigDigs;
static const double kNsPerSecd = 1000000000.0;
static const LONGLONG kNsPerMillisec = 1000000;
// ----------------------------------------------------------------------------
// Global constants
// ----------------------------------------------------------------------------
// Tolerance to failures settings.
//
// What is the interval we want to have failure free.
// in [ms]
static const uint32_t kFailureFreeInterval = 5000;
// How many failures we are willing to tolerate in the interval.
static const uint32_t kMaxFailuresPerInterval = 4;
// What is the threshold to treat fluctuations as actual failures.
// in [ms]
static const uint32_t kFailureThreshold = 50;
// If we are not able to get the value of GTC time increment, use this value
// which is the most usual increment.
static const DWORD kDefaultTimeIncrement = 156001;
// ----------------------------------------------------------------------------
// Global variables, not changing at runtime
// ----------------------------------------------------------------------------
// Result of QueryPerformanceFrequency
// We use default of 1 for the case we can't use QueryPerformanceCounter
// to make mt/ms conversions work despite that.
static uint64_t sFrequencyPerSec = 1;
namespace mozilla {
MFBT_API uint64_t GetQueryPerformanceFrequencyPerSec() {
return sFrequencyPerSec;
}
} // namespace mozilla
// How much we are tolerant to GTC occasional loose of resoltion.
// This number says how many multiples of the minimal GTC resolution
// detected on the system are acceptable. This number is empirical.
static const LONGLONG kGTCTickLeapTolerance = 4;
// Base tolerance (more: "inability of detection" range) threshold is calculated
// dynamically, and kept in sGTCResolutionThreshold.
//
// Schematically, QPC worked "100%" correctly if ((GTC_now - GTC_epoch) -
// (QPC_now - QPC_epoch)) was in [-sGTCResolutionThreshold,
// sGTCResolutionThreshold] interval every time we'd compared two time stamps.
// If not, then we check the overflow behind this basic threshold
// is in kFailureThreshold. If not, we condider it as a QPC failure. If too
// many failures in short time are detected, QPC is considered faulty and
// disabled.
//
// Kept in [mt]
static LONGLONG sGTCResolutionThreshold;
// If QPC is found faulty for two stamps in this interval, we engage
// the fault detection algorithm. For duration larger then this limit
// we bypass using durations calculated from QPC when jitter is detected,
// but don't touch the sUseQPC flag.
//
// Value is in [ms].
static const uint32_t kHardFailureLimit = 2000;
// Conversion to [mt]
static LONGLONG sHardFailureLimit;
// Conversion of kFailureFreeInterval and kFailureThreshold to [mt]
static LONGLONG sFailureFreeInterval;
static LONGLONG sFailureThreshold;
// ----------------------------------------------------------------------------
// Systemm status flags
// ----------------------------------------------------------------------------
// Flag for stable TSC that indicates platform where QPC is stable.
static bool sHasStableTSC = false;
// ----------------------------------------------------------------------------
// Global state variables, changing at runtime
// ----------------------------------------------------------------------------
// Initially true, set to false when QPC is found unstable and never
// returns back to true since that time.
static bool volatile sUseQPC = true;
// ----------------------------------------------------------------------------
// Global lock
// ----------------------------------------------------------------------------
// Thread spin count before entering the full wait state for sTimeStampLock.
// Inspired by Rob Arnold's work on PRMJ_Now().
static const DWORD kLockSpinCount = 4096;
// Common mutex (thanks the relative complexity of the logic, this is better
// then using CMPXCHG8B.)
// It is protecting the globals bellow.
static CRITICAL_SECTION sTimeStampLock;
// ----------------------------------------------------------------------------
// Global lock protected variables
// ----------------------------------------------------------------------------
// Timestamp in future until QPC must behave correctly.
// Set to now + kFailureFreeInterval on first QPC failure detection.
// Set to now + E * kFailureFreeInterval on following errors,
// where E is number of errors detected during last kFailureFreeInterval
// milliseconds, calculated simply as:
// E = (sFaultIntoleranceCheckpoint - now) / kFailureFreeInterval + 1.
// When E > kMaxFailuresPerInterval -> disable QPC.
//
// Kept in [mt]
static ULONGLONG sFaultIntoleranceCheckpoint = 0;
namespace mozilla {
// Result is in [mt]
static inline ULONGLONG PerformanceCounter() {
LARGE_INTEGER pc;
::QueryPerformanceCounter(&pc);
// QueryPerformanceCounter may slightly jitter (not be 100% monotonic.)
// This is a simple go-backward protection for such a faulty hardware.
AutoCriticalSection lock(&sTimeStampLock);
static decltype(LARGE_INTEGER::QuadPart) last;
if (last > pc.QuadPart) {
return last * 1000ULL;
}
last = pc.QuadPart;
return pc.QuadPart * 1000ULL;
}
static void InitThresholds() {
DWORD timeAdjustment = 0, timeIncrement = 0;
BOOL timeAdjustmentDisabled;
GetSystemTimeAdjustment(&timeAdjustment, &timeIncrement,
&timeAdjustmentDisabled);
LOG(("TimeStamp: timeIncrement=%d [100ns]", timeIncrement));
if (!timeIncrement) {
timeIncrement = kDefaultTimeIncrement;
}
// Ceiling to a millisecond
// Example values: 156001, 210000
DWORD timeIncrementCeil = timeIncrement;
// Don't want to round up if already rounded, values will be: 156000, 209999
timeIncrementCeil -= 1;
// Convert to ms, values will be: 15, 20
timeIncrementCeil /= 10000;
// Round up, values will be: 16, 21
timeIncrementCeil += 1;
// Convert back to 100ns, values will be: 160000, 210000
timeIncrementCeil *= 10000;
// How many milli-ticks has the interval rounded up
LONGLONG ticksPerGetTickCountResolutionCeiling =
(int64_t(timeIncrementCeil) * sFrequencyPerSec) / 10000LL;
// GTC may jump by 32 (2*16) ms in two steps, therefor use the ceiling value.
sGTCResolutionThreshold =
LONGLONG(kGTCTickLeapTolerance * ticksPerGetTickCountResolutionCeiling);
sHardFailureLimit = ms2mt(kHardFailureLimit);
sFailureFreeInterval = ms2mt(kFailureFreeInterval);
sFailureThreshold = ms2mt(kFailureThreshold);
}
static void InitResolution() {
// 10 total trials is arbitrary: what we're trying to avoid by
// looping is getting unlucky and being interrupted by a context
// switch or signal, or being bitten by paging/cache effects
ULONGLONG minres = ~0ULL;
if (sUseQPC) {
int loops = 10;
do {
ULONGLONG start = PerformanceCounter();
ULONGLONG end = PerformanceCounter();
ULONGLONG candidate = (end - start);
if (candidate < minres) {
minres = candidate;
}
} while (--loops && minres);
if (0 == minres) {
minres = 1;
}
} else {
// GetTickCount has only ~16ms known resolution
minres = ms2mt(16);
}
// Converting minres that is in [mt] to nanosecods, multiplicating
// the argument to preserve resolution.
ULONGLONG result = mt2ms(minres * kNsPerMillisec);
if (0 == result) {
result = 1;
}
sResolution = result;
// find the number of significant digits in mResolution, for the
// sake of ToSecondsSigDigits()
ULONGLONG sigDigs;
for (sigDigs = 1; !(sigDigs == result || 10 * sigDigs > result);
sigDigs *= 10)
;
sResolutionSigDigs = sigDigs;
}
// ----------------------------------------------------------------------------
// TimeStampValue implementation
// ----------------------------------------------------------------------------
MFBT_API
TimeStampValue::TimeStampValue(ULONGLONG aGTC, ULONGLONG aQPC, bool aHasQPC)
: mGTC(aGTC), mQPC(aQPC), mHasQPC(aHasQPC) {
mIsNull = aGTC == 0 && aQPC == 0;
}
MFBT_API TimeStampValue& TimeStampValue::operator+=(const int64_t aOther) {
mGTC += aOther;
mQPC += aOther;
return *this;
}
MFBT_API TimeStampValue& TimeStampValue::operator-=(const int64_t aOther) {
mGTC -= aOther;
mQPC -= aOther;
return *this;
}
// If the duration is less then two seconds, perform check of QPC stability
// by comparing both GTC and QPC calculated durations of this and aOther.
MFBT_API uint64_t TimeStampValue::CheckQPC(const TimeStampValue& aOther) const {
uint64_t deltaGTC = mGTC - aOther.mGTC;
if (!mHasQPC || !aOther.mHasQPC) { // Both not holding QPC
return deltaGTC;
}
uint64_t deltaQPC = mQPC - aOther.mQPC;
if (sHasStableTSC) { // For stable TSC there is no need to check
return deltaQPC;
}
// Check QPC is sane before using it.
int64_t diff = DeprecatedAbs(int64_t(deltaQPC) - int64_t(deltaGTC));
if (diff <= sGTCResolutionThreshold) {
return deltaQPC;
}
// Treat absolutely for calibration purposes
int64_t duration = DeprecatedAbs(int64_t(deltaGTC));
int64_t overflow = diff - sGTCResolutionThreshold;
LOG(("TimeStamp: QPC check after %llums with overflow %1.4fms",
mt2ms(duration), mt2ms_f(overflow)));
if (overflow <= sFailureThreshold) { // We are in the limit, let go.
return deltaQPC;
}
// QPC deviates, don't use it, since now this method may only return deltaGTC.
if (!sUseQPC) { // QPC already disabled, no need to run the fault tolerance
// algorithm.
return deltaGTC;
}
LOG(("TimeStamp: QPC jittered over failure threshold"));
if (duration < sHardFailureLimit) {
// Interval between the two time stamps is very short, consider
// QPC as unstable and record a failure.
uint64_t now = ms2mt(GetTickCount64());
AutoCriticalSection lock(&sTimeStampLock);
if (sFaultIntoleranceCheckpoint && sFaultIntoleranceCheckpoint > now) {
// There's already been an error in the last fault intollerant interval.
// Time since now to the checkpoint actually holds information on how many
// failures there were in the failure free interval we have defined.
uint64_t failureCount =
(sFaultIntoleranceCheckpoint - now + sFailureFreeInterval - 1) /
sFailureFreeInterval;
if (failureCount > kMaxFailuresPerInterval) {
sUseQPC = false;
LOG(("TimeStamp: QPC disabled"));
} else {
// Move the fault intolerance checkpoint more to the future, prolong it
// to reflect the number of detected failures.
++failureCount;
sFaultIntoleranceCheckpoint = now + failureCount * sFailureFreeInterval;
LOG(("TimeStamp: recording %dth QPC failure", failureCount));
}
} else {
// Setup fault intolerance checkpoint in the future for first detected
// error.
sFaultIntoleranceCheckpoint = now + sFailureFreeInterval;
LOG(("TimeStamp: recording 1st QPC failure"));
}
}
return deltaGTC;
}
MFBT_API uint64_t
TimeStampValue::operator-(const TimeStampValue& aOther) const {
if (IsNull() && aOther.IsNull()) {
return uint64_t(0);
}
return CheckQPC(aOther);
}
// ----------------------------------------------------------------------------
// TimeDuration and TimeStamp implementation
// ----------------------------------------------------------------------------
MFBT_API double BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks) {
// Converting before arithmetic avoids blocked store forward
return double(aTicks) / (double(sFrequencyPerSec) * 1000.0);
}
MFBT_API double BaseTimeDurationPlatformUtils::ToSecondsSigDigits(
int64_t aTicks) {
// don't report a value < mResolution ...
LONGLONG resolution = sResolution;
LONGLONG resolutionSigDigs = sResolutionSigDigs;
LONGLONG valueSigDigs = resolution * (aTicks / resolution);
// and chop off insignificant digits
valueSigDigs = resolutionSigDigs * (valueSigDigs / resolutionSigDigs);
return double(valueSigDigs) / kNsPerSecd;
}
MFBT_API int64_t
BaseTimeDurationPlatformUtils::TicksFromMilliseconds(double aMilliseconds) {
double result = ms2mt(aMilliseconds);
if (result > double(INT64_MAX)) {
return INT64_MAX;
} else if (result < double(INT64_MIN)) {
return INT64_MIN;
}
return result;
}
MFBT_API int64_t BaseTimeDurationPlatformUtils::ResolutionInTicks() {
return static_cast<int64_t>(sResolution);
}
static bool HasStableTSC() {
#if defined(_M_ARM64)
// AArch64 defines that its system counter run at a constant rate
// regardless of the current clock frequency of the system. See "The
// Generic Timer", section D7, in the ARMARM for ARMv8.
return true;
#else
union {
int regs[4];
struct {
int nIds;
char cpuString[12];
};
} cpuInfo;
__cpuid(cpuInfo.regs, 0);
// Only allow Intel or AMD CPUs for now.
// The order of the registers is reg[1], reg[3], reg[2]. We just adjust the
// string so that we can compare in one go.
if (_strnicmp(cpuInfo.cpuString, "GenuntelineI", sizeof(cpuInfo.cpuString)) &&
_strnicmp(cpuInfo.cpuString, "AuthcAMDenti", sizeof(cpuInfo.cpuString))) {
return false;
}
int regs[4];
// detect if the Advanced Power Management feature is supported
__cpuid(regs, 0x80000000);
if ((unsigned int)regs[0] < 0x80000007) {
// XXX should we return true here? If there is no APM there may be
// no way how TSC can run out of sync among cores.
return false;
}
__cpuid(regs, 0x80000007);
// if bit 8 is set than TSC will run at a constant rate
// in all ACPI P-states, C-states and T-states
return regs[3] & (1 << 8);
#endif
}
static bool gInitialized = false;
MFBT_API void TimeStamp::Startup() {
if (gInitialized) {
return;
}
gInitialized = true;
// Decide which implementation to use for the high-performance timer.
InitializeCriticalSectionAndSpinCount(&sTimeStampLock, kLockSpinCount);
bool forceGTC = false;
bool forceQPC = false;
char* modevar = getenv("MOZ_TIMESTAMP_MODE");
if (modevar) {
if (!strcmp(modevar, "QPC")) {
forceQPC = true;
} else if (!strcmp(modevar, "GTC")) {
forceGTC = true;
}
}
LARGE_INTEGER freq;
sUseQPC = !forceGTC && ::QueryPerformanceFrequency(&freq);
if (!sUseQPC) {
// No Performance Counter. Fall back to use GetTickCount64.
InitResolution();
LOG(("TimeStamp: using GetTickCount64"));
return;
}
sHasStableTSC = forceQPC || HasStableTSC();
LOG(("TimeStamp: HasStableTSC=%d", sHasStableTSC));
sFrequencyPerSec = freq.QuadPart;
LOG(("TimeStamp: QPC frequency=%llu", sFrequencyPerSec));
InitThresholds();
InitResolution();
return;
}
MFBT_API void TimeStamp::Shutdown() { DeleteCriticalSection(&sTimeStampLock); }
TimeStampValue NowInternal(bool aHighResolution) {
// sUseQPC is volatile
bool useQPC = (aHighResolution && sUseQPC);
// Both values are in [mt] units.
ULONGLONG QPC = useQPC ? PerformanceCounter() : uint64_t(0);
ULONGLONG GTC = ms2mt(GetTickCount64());
return TimeStampValue(GTC, QPC, useQPC);
}
MFBT_API TimeStamp TimeStamp::Now(bool aHighResolution) {
return TimeStamp(NowInternal(aHighResolution));
}
// Computes and returns the process uptime in microseconds.
// Returns 0 if an error was encountered.
MFBT_API uint64_t TimeStamp::ComputeProcessUptime() {
FILETIME start, foo, bar, baz;
bool success = GetProcessTimes(GetCurrentProcess(), &start, &foo, &bar, &baz);
if (!success) {
return 0;
}
static const StaticDynamicallyLinkedFunctionPtr<void(WINAPI*)(LPFILETIME)>
pGetSystemTimePreciseAsFileTime(L"kernel32.dll",
"GetSystemTimePreciseAsFileTime");
FILETIME now;
if (pGetSystemTimePreciseAsFileTime) {
pGetSystemTimePreciseAsFileTime(&now);
} else {
GetSystemTimeAsFileTime(&now);
}
ULARGE_INTEGER startUsec = {{start.dwLowDateTime, start.dwHighDateTime}};
ULARGE_INTEGER nowUsec = {{now.dwLowDateTime, now.dwHighDateTime}};
return (nowUsec.QuadPart - startUsec.QuadPart) / 10ULL;
}
} // namespace mozilla