yuzu/src/common/x64/native_clock.cpp

// SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#include <array>
#include <chrono>
#include <thread>

#include "common/atomic_ops.h"
#include "common/steady_clock.h"
#include "common/uint128.h"
#include "common/x64/native_clock.h"

#ifdef _MSC_VER
#include <intrin.h>
#endif

namespace Common {

#ifdef _MSC_VER
__forceinline static u64 FencedRDTSC() {
    _mm_lfence();
    _ReadWriteBarrier();
    const u64 result = __rdtsc();
    _mm_lfence();
    _ReadWriteBarrier();
    return result;
}
#else
static u64 FencedRDTSC() {
    u64 result;
    asm volatile("lfence\n\t"
                 "rdtsc\n\t"
                 "shl $32, %%rdx\n\t"
                 "or %%rdx, %0\n\t"
                 "lfence"
                 : "=a"(result)
                 :
                 : "rdx", "memory", "cc");
    return result;
}
#endif

template <u64 Nearest>
static u64 RoundToNearest(u64 value) {
    const auto mod = value % Nearest;
    return mod >= (Nearest / 2) ? (value - mod + Nearest) : (value - mod);
}

u64 EstimateRDTSCFrequency() {
    // Discard the first result measuring the rdtsc.
    FencedRDTSC();
    std::this_thread::sleep_for(std::chrono::milliseconds{1});
    FencedRDTSC();

    // Get the current time.
    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::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);
    return RoundToNearest<1000>(tsc_freq);
}

namespace X64 {
NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequency_,
                         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;
    CalculateAndSetFactors();
}

u64 NativeClock::GetRTSC() {
    TimePoint new_time_point{};
    TimePoint current_time_point{};

    current_time_point.pack = Common::AtomicLoad128(time_point.pack.data());
    do {
        const u64 current_measure = FencedRDTSC();
        u64 diff = current_measure - current_time_point.inner.last_measure;
        diff = diff & ~static_cast<u64>(static_cast<s64>(diff) >> 63); // max(diff, 0)
        new_time_point.inner.last_measure = current_measure > current_time_point.inner.last_measure
                                                ? current_measure
                                                : current_time_point.inner.last_measure;
        new_time_point.inner.accumulated_ticks = current_time_point.inner.accumulated_ticks + diff;
    } while (!Common::AtomicCompareAndSwap(time_point.pack.data(), new_time_point.pack,
                                           current_time_point.pack, current_time_point.pack));
    return new_time_point.inner.accumulated_ticks;
}

void NativeClock::Pause(bool is_paused) {
    if (!is_paused) {
        TimePoint current_time_point{};
        TimePoint new_time_point{};

        current_time_point.pack = Common::AtomicLoad128(time_point.pack.data());
        do {
            new_time_point.pack = current_time_point.pack;
            new_time_point.inner.last_measure = FencedRDTSC();
        } while (!Common::AtomicCompareAndSwap(time_point.pack.data(), new_time_point.pack,
                                               current_time_point.pack, current_time_point.pack));
    }
}

std::chrono::nanoseconds NativeClock::GetTimeNS() {
    const u64 rtsc_value = GetRTSC();
    return std::chrono::nanoseconds{MultiplyHigh(rtsc_value, ns_rtsc_factor)};
}

std::chrono::microseconds NativeClock::GetTimeUS() {
    const u64 rtsc_value = GetRTSC();
    return std::chrono::microseconds{MultiplyHigh(rtsc_value, us_rtsc_factor)};
}

std::chrono::milliseconds NativeClock::GetTimeMS() {
    const u64 rtsc_value = GetRTSC();
    return std::chrono::milliseconds{MultiplyHigh(rtsc_value, ms_rtsc_factor)};
}

u64 NativeClock::GetClockCycles() {
    const u64 rtsc_value = GetRTSC();
    return MultiplyHigh(rtsc_value, clock_rtsc_factor);
}

u64 NativeClock::GetCPUCycles() {
    const u64 rtsc_value = GetRTSC();
    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