X86/NativeClock: Improve performance of clock calculations on hot path.

This commit is contained in:
Fernando Sahmkow 2021-01-01 23:28:55 +01:00
parent 9e109849ff
commit d4f871cb6a
2 changed files with 71 additions and 5 deletions

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

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@ -41,6 +41,13 @@ private:
u64 last_measure{};
u64 accumulated_ticks{};
u64 rtsc_frequency;
// factors
u64 ns_rtsc_factor{};
u64 us_rtsc_factor{};
u64 ms_rtsc_factor{};
u64 clock_rtsc_factor{};
u64 cpu_rtsc_factor{};
};
} // namespace X64