From dcd13a7566340e80c042da7f626f9747ac71b8a7 Mon Sep 17 00:00:00 2001 From: Morph <39850852+Morph1984@users.noreply.github.com> Date: Sat, 4 Mar 2023 21:44:31 -0500 Subject: [PATCH] native_clock: Re-adjust the RDTSC frequency The RDTSC frequency reported by CPUID is not accurate to its true frequency. We will spawn a separate thread to calculate the true RDTSC frequency after a measurement period of 30 seconds has elapsed. --- src/common/x64/native_clock.cpp | 34 ++++++++++++++++++++++++++++----- src/common/x64/native_clock.h | 5 +++++ 2 files changed, 34 insertions(+), 5 deletions(-) diff --git a/src/common/x64/native_clock.cpp b/src/common/x64/native_clock.cpp index bc1a973b0..c11590291 100644 --- a/src/common/x64/native_clock.cpp +++ b/src/common/x64/native_clock.cpp @@ -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 30 seconds has elapsed. + time_sync_thread = std::jthread{[this](std::stop_token token) { + // Get the current time. + const auto start_time = Common::SteadyClock::Now(); + const u64 tsc_start = FencedRDTSC(); + // Wait for 30 seconds. + if (!Common::StoppableTimedWait(token, std::chrono::seconds{30})) { + return; + } + const auto end_time = Common::SteadyClock::Now(); + const u64 tsc_end = FencedRDTSC(); + // Calculate differences. + const u64 timer_diff = static_cast( + std::chrono::duration_cast(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 diff --git a/src/common/x64/native_clock.h b/src/common/x64/native_clock.h index 38ae7a462..03ca291d8 100644 --- a/src/common/x64/native_clock.h +++ b/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