X86/NativeClock: Improve performance of clock calculations on hot path.
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@ -2,12 +2,17 @@
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// Licensed under GPLv2 or any later version
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// Refer to the license.txt file included.
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#include <array>
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#include <chrono>
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#include <limits>
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#include <mutex>
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#include <thread>
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#ifdef _MSC_VER
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#include <intrin.h>
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#pragma intrinsic(__umulh)
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#pragma intrinsic(_udiv128)
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#else
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#include <x86intrin.h>
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#endif
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@ -15,6 +20,55 @@
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#include "common/uint128.h"
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#include "common/x64/native_clock.h"
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namespace {
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[[nodiscard]] u64 GetFixedPoint64Factor(u64 numerator, u64 divisor) {
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#ifdef __SIZEOF_INT128__
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const auto base = static_cast<unsigned __int128>(numerator) << 64ULL;
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return static_cast<u64>(base / divisor);
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#elif defined(_M_X64) || defined(_M_ARM64)
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std::array<u64, 2> r = {0, numerator};
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u64 remainder;
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#if _MSC_VER < 1923
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return udiv128(r[1], r[0], divisor, &remainder);
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#else
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return _udiv128(r[1], r[0], divisor, &remainder);
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#endif
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#else
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// This one is bit more inaccurate.
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return MultiplyAndDivide64(std::numeric_limits<u64>::max(), numerator, divisor);
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#endif
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}
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[[nodiscard]] u64 MultiplyHigh(u64 a, u64 b) {
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#ifdef __SIZEOF_INT128__
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return (static_cast<unsigned __int128>(a) * static_cast<unsigned __int128>(b)) >> 64;
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#elif defined(_M_X64) || defined(_M_ARM64)
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return __umulh(a, b); // MSVC
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#else
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// Generic fallback
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const u64 a_lo = u32(a);
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const u64 a_hi = a >> 32;
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const u64 b_lo = u32(b);
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const u64 b_hi = b >> 32;
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const u64 a_x_b_hi = a_hi * b_hi;
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const u64 a_x_b_mid = a_hi * b_lo;
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const u64 b_x_a_mid = b_hi * a_lo;
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const u64 a_x_b_lo = a_lo * b_lo;
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const u64 carry_bit = (static_cast<u64>(static_cast<u32>(a_x_b_mid)) +
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static_cast<u64>(static_cast<u32>(b_x_a_mid)) + (a_x_b_lo >> 32)) >>
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32;
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const u64 multhi = a_x_b_hi + (a_x_b_mid >> 32) + (b_x_a_mid >> 32) + carry_bit;
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return multhi;
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#endif
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}
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} // namespace
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namespace Common {
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u64 EstimateRDTSCFrequency() {
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@ -50,6 +104,11 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen
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_mm_mfence();
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last_measure = __rdtsc();
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accumulated_ticks = 0U;
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ns_rtsc_factor = GetFixedPoint64Factor(1000000000, rtsc_frequency);
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us_rtsc_factor = GetFixedPoint64Factor(1000000, rtsc_frequency);
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ms_rtsc_factor = GetFixedPoint64Factor(1000, rtsc_frequency);
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clock_rtsc_factor = GetFixedPoint64Factor(emulated_clock_frequency, rtsc_frequency);
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cpu_rtsc_factor = GetFixedPoint64Factor(emulated_cpu_frequency, rtsc_frequency);
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}
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u64 NativeClock::GetRTSC() {
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@ -75,27 +134,27 @@ void NativeClock::Pause(bool is_paused) {
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std::chrono::nanoseconds NativeClock::GetTimeNS() {
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const u64 rtsc_value = GetRTSC();
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return std::chrono::nanoseconds{MultiplyAndDivide64(rtsc_value, 1000000000, rtsc_frequency)};
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return std::chrono::nanoseconds{MultiplyHigh(rtsc_value, ns_rtsc_factor)};
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}
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std::chrono::microseconds NativeClock::GetTimeUS() {
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const u64 rtsc_value = GetRTSC();
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return std::chrono::microseconds{MultiplyAndDivide64(rtsc_value, 1000000, rtsc_frequency)};
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return std::chrono::microseconds{MultiplyHigh(rtsc_value, us_rtsc_factor)};
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}
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std::chrono::milliseconds NativeClock::GetTimeMS() {
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const u64 rtsc_value = GetRTSC();
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return std::chrono::milliseconds{MultiplyAndDivide64(rtsc_value, 1000, rtsc_frequency)};
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return std::chrono::milliseconds{MultiplyHigh(rtsc_value, ms_rtsc_factor)};
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}
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u64 NativeClock::GetClockCycles() {
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const u64 rtsc_value = GetRTSC();
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return MultiplyAndDivide64(rtsc_value, emulated_clock_frequency, rtsc_frequency);
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return MultiplyHigh(rtsc_value, clock_rtsc_factor);
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}
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u64 NativeClock::GetCPUCycles() {
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const u64 rtsc_value = GetRTSC();
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return MultiplyAndDivide64(rtsc_value, emulated_cpu_frequency, rtsc_frequency);
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return MultiplyHigh(rtsc_value, cpu_rtsc_factor);
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}
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} // namespace X64
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@ -41,6 +41,13 @@ private:
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u64 last_measure{};
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u64 accumulated_ticks{};
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u64 rtsc_frequency;
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// factors
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u64 ns_rtsc_factor{};
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u64 us_rtsc_factor{};
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u64 ms_rtsc_factor{};
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u64 clock_rtsc_factor{};
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u64 cpu_rtsc_factor{};
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};
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} // namespace X64
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