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 bc1a973b06..c11590291b 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<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
diff --git a/src/common/x64/native_clock.h b/src/common/x64/native_clock.h
index 38ae7a4625..03ca291d80 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