From 4e766280c4481d23a64a1c80c0ec40d7cf1ff378 Mon Sep 17 00:00:00 2001 From: Morph <39850852+Morph1984@users.noreply.github.com> Date: Sun, 30 Jan 2022 12:36:56 -0500 Subject: [PATCH 1/2] common: wall_clock: Utilize constants for ms, us, and ns ratios --- src/common/wall_clock.cpp | 4 ++-- src/common/wall_clock.h | 4 ++++ src/common/x64/native_clock.cpp | 6 +++--- 3 files changed, 9 insertions(+), 5 deletions(-) diff --git a/src/common/wall_clock.cpp b/src/common/wall_clock.cpp index ffa282e88..081e0562f 100644 --- a/src/common/wall_clock.cpp +++ b/src/common/wall_clock.cpp @@ -73,8 +73,8 @@ std::unique_ptr CreateBestMatchingClock(u32 emulated_cpu_frequency, rtsc_frequency = EstimateRDTSCFrequency(); } - // Fallback to StandardWallClock if rtsc period is higher than a nano second - if (rtsc_frequency <= 1000000000) { + // Fallback to StandardWallClock if the hardware TSC does not have nanosecond precision. + if (rtsc_frequency <= WallClock::NS_RATIO) { return std::make_unique(emulated_cpu_frequency, emulated_clock_frequency); } else { diff --git a/src/common/wall_clock.h b/src/common/wall_clock.h index cef3e9499..4d132c531 100644 --- a/src/common/wall_clock.h +++ b/src/common/wall_clock.h @@ -13,6 +13,10 @@ namespace Common { class WallClock { public: + static constexpr u64 NS_RATIO = 1'000'000'000; + static constexpr u64 US_RATIO = 1'000'000; + static constexpr u64 MS_RATIO = 1'000; + virtual ~WallClock() = default; /// Returns current wall time in nanoseconds diff --git a/src/common/x64/native_clock.cpp b/src/common/x64/native_clock.cpp index 82ee2c8a1..91b842829 100644 --- a/src/common/x64/native_clock.cpp +++ b/src/common/x64/native_clock.cpp @@ -47,9 +47,9 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen _mm_mfence(); time_point.inner.last_measure = __rdtsc(); time_point.inner.accumulated_ticks = 0U; - ns_rtsc_factor = GetFixedPoint64Factor(1000000000, rtsc_frequency); - us_rtsc_factor = GetFixedPoint64Factor(1000000, rtsc_frequency); - ms_rtsc_factor = GetFixedPoint64Factor(1000, rtsc_frequency); + 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); } From 6267110b694d3b3f8a8561c61ad6b4a4548873b5 Mon Sep 17 00:00:00 2001 From: Morph <39850852+Morph1984@users.noreply.github.com> Date: Sun, 30 Jan 2022 12:57:23 -0500 Subject: [PATCH 2/2] common: wall_clock: Check precision against the emulated CPU and CNTFRQ In addition to requiring nanosecond precision, using the native clock requires that the hardware TSC has a precision greater than the emulated CPU and its clock counter. --- src/common/wall_clock.cpp | 16 ++++++++++------ src/common/wall_clock.h | 4 ++-- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/src/common/wall_clock.cpp b/src/common/wall_clock.cpp index 081e0562f..9acf7551e 100644 --- a/src/common/wall_clock.cpp +++ b/src/common/wall_clock.cpp @@ -65,16 +65,20 @@ private: #ifdef ARCHITECTURE_x86_64 -std::unique_ptr CreateBestMatchingClock(u32 emulated_cpu_frequency, - u32 emulated_clock_frequency) { +std::unique_ptr CreateBestMatchingClock(u64 emulated_cpu_frequency, + u64 emulated_clock_frequency) { const auto& caps = GetCPUCaps(); u64 rtsc_frequency = 0; if (caps.invariant_tsc) { rtsc_frequency = EstimateRDTSCFrequency(); } - // Fallback to StandardWallClock if the hardware TSC does not have nanosecond precision. - if (rtsc_frequency <= WallClock::NS_RATIO) { + // Fallback to StandardWallClock if the hardware TSC does not have the precision greater than: + // - A nanosecond + // - The emulated CPU frequency + // - The emulated clock counter frequency (CNTFRQ) + if (rtsc_frequency <= WallClock::NS_RATIO || rtsc_frequency <= emulated_cpu_frequency || + rtsc_frequency <= emulated_clock_frequency) { return std::make_unique(emulated_cpu_frequency, emulated_clock_frequency); } else { @@ -85,8 +89,8 @@ std::unique_ptr CreateBestMatchingClock(u32 emulated_cpu_frequency, #else -std::unique_ptr CreateBestMatchingClock(u32 emulated_cpu_frequency, - u32 emulated_clock_frequency) { +std::unique_ptr CreateBestMatchingClock(u64 emulated_cpu_frequency, + u64 emulated_clock_frequency) { return std::make_unique(emulated_cpu_frequency, emulated_clock_frequency); } diff --git a/src/common/wall_clock.h b/src/common/wall_clock.h index 4d132c531..874448c27 100644 --- a/src/common/wall_clock.h +++ b/src/common/wall_clock.h @@ -53,7 +53,7 @@ private: bool is_native; }; -[[nodiscard]] std::unique_ptr CreateBestMatchingClock(u32 emulated_cpu_frequency, - u32 emulated_clock_frequency); +[[nodiscard]] std::unique_ptr CreateBestMatchingClock(u64 emulated_cpu_frequency, + u64 emulated_clock_frequency); } // namespace Common