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