Merge pull request #9917 from Morph1984/the-real-time

native_clock: Re-adjust the RDTSC frequency to its real frequency

src/common/steady_clock.cpp

@@ -23,6 +23,19 @@ static s64 WindowsQueryPerformanceCounter() {
     QueryPerformanceCounter(&counter);
     return counter.QuadPart;
 }
+
+static s64 GetSystemTimeNS() {
+    // GetSystemTimePreciseAsFileTime returns the file time in 100ns units.
+    static constexpr s64 Multiplier = 100;
+    // Convert Windows epoch to Unix epoch.
+    static constexpr s64 WindowsEpochToUnixEpochNS = 0x19DB1DED53E8000LL;
+
+    FILETIME filetime;
+    GetSystemTimePreciseAsFileTime(&filetime);
+    return Multiplier * ((static_cast<s64>(filetime.dwHighDateTime) << 32) +
+                         static_cast<s64>(filetime.dwLowDateTime)) -
+           WindowsEpochToUnixEpochNS;
+}
 #endif
 
 SteadyClock::time_point SteadyClock::Now() noexcept {
@@ -53,4 +66,16 @@ SteadyClock::time_point SteadyClock::Now() noexcept {
 #endif
 }
 
+RealTimeClock::time_point RealTimeClock::Now() noexcept {
+#if defined(_WIN32)
+    return time_point{duration{GetSystemTimeNS()}};
+#elif defined(__APPLE__)
+    return time_point{duration{clock_gettime_nsec_np(CLOCK_REALTIME)}};
+#else
+    timespec ts;
+    clock_gettime(CLOCK_REALTIME, &ts);
+    return time_point{std::chrono::seconds{ts.tv_sec} + std::chrono::nanoseconds{ts.tv_nsec}};
+#endif
+}
+
 }; // namespace Common

src/common/steady_clock.h

@@ -20,4 +20,15 @@ struct SteadyClock {
     [[nodiscard]] static time_point Now() noexcept;
 };
 
+struct RealTimeClock {
+    using rep = s64;
+    using period = std::nano;
+    using duration = std::chrono::nanoseconds;
+    using time_point = std::chrono::time_point<RealTimeClock>;
+
+    static constexpr bool is_steady = false;
+
+    [[nodiscard]] static time_point Now() noexcept;
+};
+
 } // namespace Common

src/common/x64/native_clock.cpp

@@ -53,11 +53,11 @@ u64 EstimateRDTSCFrequency() {
     FencedRDTSC();
 
     // Get the current time.
-    const auto start_time = Common::SteadyClock::Now();
+    const auto start_time = Common::RealTimeClock::Now();
     const u64 tsc_start = FencedRDTSC();
     // Wait for 250 milliseconds.
     std::this_thread::sleep_for(std::chrono::milliseconds{250});
-    const auto end_time = Common::SteadyClock::Now();
+    const auto end_time = Common::RealTimeClock::Now();
     const u64 tsc_end = FencedRDTSC();
     // Calculate differences.
     const u64 timer_diff = static_cast<u64>(
@@ -72,13 +72,29 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen
                          u64 rtsc_frequency_)
     : WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, true), rtsc_frequency{
                                                                                rtsc_frequency_} {
+    // Thread to re-adjust the RDTSC frequency after 10 seconds has elapsed.
+    time_sync_thread = std::jthread{[this](std::stop_token token) {
+        // Get the current time.
+        const auto start_time = Common::RealTimeClock::Now();
+        const u64 tsc_start = FencedRDTSC();
+        // Wait for 10 seconds.
+        if (!Common::StoppableTimedWait(token, std::chrono::seconds{10})) {
+            return;
+        }
+        const auto end_time = Common::RealTimeClock::Now();
+        const u64 tsc_end = FencedRDTSC();
+        // Calculate differences.
+        const u64 timer_diff = static_cast<u64>(
+            std::chrono::duration_cast<std::chrono::nanoseconds>(end_time - start_time).count());
+        const u64 tsc_diff = tsc_end - tsc_start;
+        const u64 tsc_freq = MultiplyAndDivide64(tsc_diff, 1000000000ULL, timer_diff);
+        rtsc_frequency = tsc_freq;
+        CalculateAndSetFactors();
+    }};
+
     time_point.inner.last_measure = FencedRDTSC();
     time_point.inner.accumulated_ticks = 0U;
-    ns_rtsc_factor = GetFixedPoint64Factor(NS_RATIO, rtsc_frequency);
-    us_rtsc_factor = GetFixedPoint64Factor(US_RATIO, rtsc_frequency);
-    ms_rtsc_factor = GetFixedPoint64Factor(MS_RATIO, rtsc_frequency);
-    clock_rtsc_factor = GetFixedPoint64Factor(emulated_clock_frequency, rtsc_frequency);
-    cpu_rtsc_factor = GetFixedPoint64Factor(emulated_cpu_frequency, rtsc_frequency);
+    CalculateAndSetFactors();
 }
 
 u64 NativeClock::GetRTSC() {
@@ -138,6 +154,14 @@ u64 NativeClock::GetCPUCycles() {
     return MultiplyHigh(rtsc_value, cpu_rtsc_factor);
 }
 
+void NativeClock::CalculateAndSetFactors() {
+    ns_rtsc_factor = GetFixedPoint64Factor(NS_RATIO, rtsc_frequency);
+    us_rtsc_factor = GetFixedPoint64Factor(US_RATIO, rtsc_frequency);
+    ms_rtsc_factor = GetFixedPoint64Factor(MS_RATIO, rtsc_frequency);
+    clock_rtsc_factor = GetFixedPoint64Factor(emulated_clock_frequency, rtsc_frequency);
+    cpu_rtsc_factor = GetFixedPoint64Factor(emulated_cpu_frequency, rtsc_frequency);
+}
+
 } // namespace X64
 
 } // namespace Common

src/common/x64/native_clock.h

@@ -3,6 +3,7 @@
 
 #pragma once
 
+#include "common/polyfill_thread.h"
 #include "common/wall_clock.h"
 
 namespace Common {
@@ -28,6 +29,8 @@ public:
 private:
     u64 GetRTSC();
 
+    void CalculateAndSetFactors();
+
     union alignas(16) TimePoint {
         TimePoint() : pack{} {}
         u128 pack{};
@@ -47,6 +50,8 @@ private:
     u64 ms_rtsc_factor{};
 
     u64 rtsc_frequency;
+
+    std::jthread time_sync_thread;
 };
 } // namespace X64