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Merge pull request #8143 from merryhime/rdtsc
native_clock: Use lfence with rdtsc
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commit
a02fd4cddd
@ -10,25 +10,49 @@
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#include "common/uint128.h"
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#include "common/x64/native_clock.h"
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#ifdef _MSC_VER
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#include <intrin.h>
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#endif
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namespace Common {
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#ifdef _MSC_VER
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__forceinline static u64 FencedRDTSC() {
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_mm_lfence();
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_ReadWriteBarrier();
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const u64 result = __rdtsc();
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_mm_lfence();
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_ReadWriteBarrier();
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return result;
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}
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#else
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static u64 FencedRDTSC() {
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u64 result;
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asm volatile("lfence\n\t"
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"rdtsc\n\t"
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"shl $32, %%rdx\n\t"
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"or %%rdx, %0\n\t"
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"lfence"
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: "=a"(result)
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:
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: "rdx", "memory", "cc");
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return result;
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}
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#endif
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u64 EstimateRDTSCFrequency() {
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// Discard the first result measuring the rdtsc.
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_mm_mfence();
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__rdtsc();
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FencedRDTSC();
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std::this_thread::sleep_for(std::chrono::milliseconds{1});
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_mm_mfence();
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__rdtsc();
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FencedRDTSC();
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// Get the current time.
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const auto start_time = std::chrono::steady_clock::now();
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_mm_mfence();
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const u64 tsc_start = __rdtsc();
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const u64 tsc_start = FencedRDTSC();
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// Wait for 200 milliseconds.
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std::this_thread::sleep_for(std::chrono::milliseconds{200});
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const auto end_time = std::chrono::steady_clock::now();
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_mm_mfence();
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const u64 tsc_end = __rdtsc();
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const u64 tsc_end = FencedRDTSC();
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// Calculate differences.
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const u64 timer_diff = static_cast<u64>(
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std::chrono::duration_cast<std::chrono::nanoseconds>(end_time - start_time).count());
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@ -42,8 +66,7 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen
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u64 rtsc_frequency_)
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: WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, true), rtsc_frequency{
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rtsc_frequency_} {
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_mm_mfence();
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time_point.inner.last_measure = __rdtsc();
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time_point.inner.last_measure = FencedRDTSC();
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time_point.inner.accumulated_ticks = 0U;
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ns_rtsc_factor = GetFixedPoint64Factor(NS_RATIO, rtsc_frequency);
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us_rtsc_factor = GetFixedPoint64Factor(US_RATIO, rtsc_frequency);
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@ -58,8 +81,7 @@ u64 NativeClock::GetRTSC() {
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current_time_point.pack = Common::AtomicLoad128(time_point.pack.data());
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do {
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_mm_mfence();
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const u64 current_measure = __rdtsc();
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const u64 current_measure = FencedRDTSC();
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u64 diff = current_measure - current_time_point.inner.last_measure;
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diff = diff & ~static_cast<u64>(static_cast<s64>(diff) >> 63); // max(diff, 0)
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new_time_point.inner.last_measure = current_measure > current_time_point.inner.last_measure
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@ -80,8 +102,7 @@ void NativeClock::Pause(bool is_paused) {
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current_time_point.pack = Common::AtomicLoad128(time_point.pack.data());
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do {
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new_time_point.pack = current_time_point.pack;
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_mm_mfence();
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new_time_point.inner.last_measure = __rdtsc();
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new_time_point.inner.last_measure = FencedRDTSC();
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} while (!Common::AtomicCompareAndSwap(time_point.pack.data(), new_time_point.pack,
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current_time_point.pack, current_time_point.pack));
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}
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