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native_clock: Re-adjust the RDTSC frequency

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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.
This commit is contained in:
Morph 2023-03-04 21:44:31 -05:00
parent a7792e5ff8
commit dcd13a7566
2 changed files with 34 additions and 5 deletions
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34
src/common/x64/native_clock.cpp
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@ -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

5
src/common/x64/native_clock.h
View file

@ -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