common: Rework timekeeping with native RDTSC and port to linux

src/common/rdtsc.cpp

@@ -0,0 +1,60 @@
+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <thread>
+#include "common/rdtsc.h"
+#include "common/uint128.h"
+
+#ifdef _WIN64
+#include <windows.h>
+#endif
+
+namespace Common {
+
+static constexpr size_t SecondToNanoseconds = 1000000000ULL;
+
+template <u64 Nearest>
+static u64 RoundToNearest(u64 value) {
+    const auto mod = value % Nearest;
+    return mod >= (Nearest / 2) ? (value - mod + Nearest) : (value - mod);
+}
+
+static u64 GetTimeNs() {
+#ifdef _WIN64
+    // GetSystemTimePreciseAsFileTime returns the file time in 100ns units.
+    static constexpr u64 Multiplier = 100;
+    // Convert Windows epoch to Unix epoch.
+    static constexpr u64 WindowsEpochToUnixEpoch = 0x19DB1DED53E8000LL;
+    FILETIME filetime;
+    GetSystemTimePreciseAsFileTime(&filetime);
+    return Multiplier * ((static_cast<u64>(filetime.dwHighDateTime) << 32) +
+                          static_cast<u64>(filetime.dwLowDateTime) - WindowsEpochToUnixEpoch);
+#elif defined(__APPLE__)
+    return clock_gettime_nsec_np(CLOCK_REALTIME);
+#else
+    timespec ts;
+    clock_gettime(CLOCK_REALTIME, &ts);
+    return ts.tv_sec * SecondToNanoseconds + ts.tv_nsec;
+#endif
+}
+
+u64 EstimateRDTSCFrequency() {
+    // Discard the first result measuring the rdtsc.
+    FencedRDTSC();
+    std::this_thread::sleep_for(std::chrono::milliseconds{1});
+    FencedRDTSC();
+
+    // Get the current time.
+    const auto start_time = GetTimeNs();
+    const u64 tsc_start = FencedRDTSC();
+    // Wait for 100 milliseconds.
+    std::this_thread::sleep_for(std::chrono::milliseconds{100});
+    const auto end_time = GetTimeNs();
+    const u64 tsc_end = FencedRDTSC();
+    // Calculate differences.
+    const u64 tsc_diff = tsc_end - tsc_start;
+    const u64 tsc_freq = MultiplyAndDivide64(tsc_diff, 1000000000ULL, end_time - start_time);
+    return RoundToNearest<100'000>(tsc_freq);
+}
+
+} // namespace Common