From fdd4d019ef6f37421358ae70f3d5e036857dd758 Mon Sep 17 00:00:00 2001
From: merry <git@mary.rs>
Date: Sat, 2 Apr 2022 21:54:39 +0100
Subject: [PATCH] native_clock: Use lfence with rdtsc
---
src/common/x64/native_clock.cpp | 47 +++++++++++++++++++++++----------
1 file changed, 33 insertions(+), 14 deletions(-)
diff --git a/src/common/x64/native_clock.cpp b/src/common/x64/native_clock.cpp
index 7a3f21dcf1..63364f839a 100644
--- a/src/common/x64/native_clock.cpp
+++ b/src/common/x64/native_clock.cpp
@@ -10,25 +10,47 @@
#include "common/uint128.h"
#include "common/x64/native_clock.h"
+#ifdef _MSC_VER
+#include <intrin.h>
+#endif
+
namespace Common {
+inline u64 FencedRDTSC() {
+#ifdef _MSC_VER
+ _mm_lfence();
+ _ReadWriteBarrier();
+ const u64 result = __rdtsc();
+ _mm_lfence();
+ _ReadWriteBarrier();
+ return result;
+#else
+ 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 +64,7 @@ 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 +79,7 @@ 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 +100,7 @@ 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));
}