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Merge pull request #8143 from merryhime/rdtsc

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native_clock: Use lfence with rdtsc
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Fernando S 2022-04-07 16:17:45 +02:00 committed by GitHub
commit a02fd4cddd
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1 changed files with 35 additions and 14 deletions
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49
src/common/x64/native_clock.cpp
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@ -10,25 +10,49 @@
#include "common/uint128.h"
#include "common/x64/native_clock.h"
#ifdef _MSC_VER
#include <intrin.h>
#endif
namespace Common {
#ifdef _MSC_VER
__forceinline static u64 FencedRDTSC() {
_mm_lfence();
_ReadWriteBarrier();
const u64 result = __rdtsc();
_mm_lfence();
_ReadWriteBarrier();
return result;
}
#else
static u64 FencedRDTSC() {
u64 result;
asm volatile("lfence\n\t"
"rdtsc\n\t"
"shl $32, %%rdx\n\t"
"or %%rdx, %0\n\t"
"lfence"
: "=a"(result)
:
: "rdx", "memory", "cc");
return result;
}
#endif
u64 EstimateRDTSCFrequency() {
// Discard the first result measuring the rdtsc.
_mm_mfence();
__rdtsc();
FencedRDTSC();
std::this_thread::sleep_for(std::chrono::milliseconds{1});
_mm_mfence();
__rdtsc();
FencedRDTSC();
// Get the current time.
const auto start_time = std::chrono::steady_clock::now();
_mm_mfence();
const u64 tsc_start = __rdtsc();
const u64 tsc_start = FencedRDTSC();
// Wait for 200 milliseconds.
std::this_thread::sleep_for(std::chrono::milliseconds{200});
const auto end_time = std::chrono::steady_clock::now();
_mm_mfence();
const u64 tsc_end = __rdtsc();
const u64 tsc_end = FencedRDTSC();
// Calculate differences.
const u64 timer_diff = static_cast<u64>(
std::chrono::duration_cast<std::chrono::nanoseconds>(end_time - start_time).count());
@ -42,8 +66,7 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen
u64 rtsc_frequency_)
: WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, true), rtsc_frequency{
rtsc_frequency_} {
_mm_mfence();
time_point.inner.last_measure = __rdtsc();
time_point.inner.last_measure = FencedRDTSC();
time_point.inner.accumulated_ticks = 0U;
ns_rtsc_factor = GetFixedPoint64Factor(NS_RATIO, rtsc_frequency);
us_rtsc_factor = GetFixedPoint64Factor(US_RATIO, rtsc_frequency);
@ -58,8 +81,7 @@ u64 NativeClock::GetRTSC() {
current_time_point.pack = Common::AtomicLoad128(time_point.pack.data());
do {
_mm_mfence();
const u64 current_measure = __rdtsc();
const u64 current_measure = FencedRDTSC();
u64 diff = current_measure - current_time_point.inner.last_measure;
diff = diff & ~static_cast<u64>(static_cast<s64>(diff) >> 63); // max(diff, 0)
new_time_point.inner.last_measure = current_measure > current_time_point.inner.last_measure
@ -80,8 +102,7 @@ void NativeClock::Pause(bool is_paused) {
current_time_point.pack = Common::AtomicLoad128(time_point.pack.data());
do {
new_time_point.pack = current_time_point.pack;
_mm_mfence();
new_time_point.inner.last_measure = __rdtsc();
new_time_point.inner.last_measure = FencedRDTSC();
} while (!Common::AtomicCompareAndSwap(time_point.pack.data(), new_time_point.pack,
current_time_point.pack, current_time_point.pack));
}