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common/x64: Use TSC clock rate from CPUID when available

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The current method used to estimate the TSC is fairly accurate - within a few kHz - but the exact value can be extracted from CPUID if available.
This commit is contained in:
Marshall Mohror 2022-07-06 12:42:01 -05:00
parent 770611fdf3
commit b2ad4dd189
3 changed files with 19 additions and 1 deletions
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2
src/common/wall_clock.cpp
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@ -67,7 +67,7 @@ std::unique_ptr<WallClock> CreateBestMatchingClock(u64 emulated_cpu_frequency,
const auto& caps = GetCPUCaps();
u64 rtsc_frequency = 0;
if (caps.invariant_tsc) {
rtsc_frequency = EstimateRDTSCFrequency();
rtsc_frequency = caps.tsc_frequency ? caps.tsc_frequency : EstimateRDTSCFrequency();
}
// Fallback to StandardWallClock if the hardware TSC does not have the precision greater than:

13
src/common/x64/cpu_detect.cpp
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@ -161,6 +161,19 @@ static CPUCaps Detect() {
caps.invariant_tsc = Common::Bit<8>(cpu_id[3]);
}
if (max_std_fn >= 0x15) {
__cpuid(cpu_id, 0x15);
caps.tsc_crystal_ratio_denominator = cpu_id[0];
caps.tsc_crystal_ratio_numerator = cpu_id[1];
caps.crystal_frequency = cpu_id[2];
// Some CPU models might not return a crystal frequency.
// The CPU model can be detected to use the values from turbostat
// https://github.com/torvalds/linux/blob/master/tools/power/x86/turbostat/turbostat.c#L5569
// but it's easier to just estimate the TSC tick rate for these cases.
caps.tsc_frequency = static_cast<u64>(caps.crystal_frequency) *
caps.tsc_crystal_ratio_numerator / caps.tsc_crystal_ratio_denominator;
}
if (max_std_fn >= 0x16) {
__cpuid(cpu_id, 0x16);
caps.base_frequency = cpu_id[0];

5
src/common/x64/cpu_detect.h
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@ -30,6 +30,11 @@ struct CPUCaps {
u32 max_frequency;
u32 bus_frequency;
u32 tsc_crystal_ratio_denominator;
u32 tsc_crystal_ratio_numerator;
u32 crystal_frequency;
u64 tsc_frequency; // Derived from the above three values
bool sse : 1;
bool sse2 : 1;
bool sse3 : 1;