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common: wall_clock: Check precision against the emulated CPU and CNTFRQ

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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.
This commit is contained in:
Morph 2022-01-30 12:57:23 -05:00
parent 4e766280c4
commit 6267110b69
2 changed files with 12 additions and 8 deletions
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16
src/common/wall_clock.cpp
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@ -65,16 +65,20 @@ private:
#ifdef ARCHITECTURE_x86_64 #ifdef ARCHITECTURE_x86_64
std::unique_ptr<WallClock> CreateBestMatchingClock(u32 emulated_cpu_frequency, std::unique_ptr<WallClock> CreateBestMatchingClock(u64 emulated_cpu_frequency,
u32 emulated_clock_frequency) { u64 emulated_clock_frequency) {
const auto& caps = GetCPUCaps(); const auto& caps = GetCPUCaps();
u64 rtsc_frequency = 0; u64 rtsc_frequency = 0;
if (caps.invariant_tsc) { if (caps.invariant_tsc) {
rtsc_frequency = EstimateRDTSCFrequency(); rtsc_frequency = EstimateRDTSCFrequency();
} }
// Fallback to StandardWallClock if the hardware TSC does not have nanosecond precision. // Fallback to StandardWallClock if the hardware TSC does not have the precision greater than:
if (rtsc_frequency <= WallClock::NS_RATIO) { // - 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<StandardWallClock>(emulated_cpu_frequency, return std::make_unique<StandardWallClock>(emulated_cpu_frequency,
emulated_clock_frequency); emulated_clock_frequency);
} else { } else {
@ -85,8 +89,8 @@ std::unique_ptr<WallClock> CreateBestMatchingClock(u32 emulated_cpu_frequency,
#else #else
std::unique_ptr<WallClock> CreateBestMatchingClock(u32 emulated_cpu_frequency, std::unique_ptr<WallClock> CreateBestMatchingClock(u64 emulated_cpu_frequency,
u32 emulated_clock_frequency) { u64 emulated_clock_frequency) {
return std::make_unique<StandardWallClock>(emulated_cpu_frequency, emulated_clock_frequency); return std::make_unique<StandardWallClock>(emulated_cpu_frequency, emulated_clock_frequency);
} }

4
src/common/wall_clock.h
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@ -53,7 +53,7 @@ private:
bool is_native; bool is_native;
}; };
[[nodiscard]] std::unique_ptr<WallClock> CreateBestMatchingClock(u32 emulated_cpu_frequency, [[nodiscard]] std::unique_ptr<WallClock> CreateBestMatchingClock(u64 emulated_cpu_frequency,
u32 emulated_clock_frequency); u64 emulated_clock_frequency);
} // namespace Common } // namespace Common