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X86/NativeClock: Reimplement RTDSC access to be lock free.

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This commit is contained in:
Fernando Sahmkow 2021-01-02 02:24:49 +01:00
parent d4f871cb6a
commit 53d92318b8
5 changed files with 107 additions and 103 deletions
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41
src/common/x64/native_clock.cpp
View file

@ -17,6 +17,7 @@
#include <x86intrin.h>
#endif
#include "common/atomic_ops.h"
#include "common/uint128.h"
#include "common/x64/native_clock.h"
@ -102,8 +103,8 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen
: WallClock(emulated_cpu_frequency_, emulated_clock_frequency_, true), rtsc_frequency{
rtsc_frequency_} {
_mm_mfence();
last_measure = __rdtsc();
accumulated_ticks = 0U;
time_point.inner.last_measure = __rdtsc();
time_point.inner.accumulated_ticks = 0U;
ns_rtsc_factor = GetFixedPoint64Factor(1000000000, rtsc_frequency);
us_rtsc_factor = GetFixedPoint64Factor(1000000, rtsc_frequency);
ms_rtsc_factor = GetFixedPoint64Factor(1000, rtsc_frequency);
@ -112,23 +113,35 @@ NativeClock::NativeClock(u64 emulated_cpu_frequency_, u64 emulated_clock_frequen
}
u64 NativeClock::GetRTSC() {
std::scoped_lock scope{rtsc_serialize};
_mm_mfence();
const u64 current_measure = __rdtsc();
u64 diff = current_measure - last_measure;
diff = diff & ~static_cast<u64>(static_cast<s64>(diff) >> 63); // max(diff, 0)
if (current_measure > last_measure) {
last_measure = current_measure;
}
accumulated_ticks += diff;
TimePoint new_time_point{};
TimePoint current_time_point{};
do {
current_time_point.pack = time_point.pack;
_mm_mfence();
const u64 current_measure = __rdtsc();
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
? current_measure
: current_time_point.inner.last_measure;
new_time_point.inner.accumulated_ticks = current_time_point.inner.accumulated_ticks + diff;
} while (!Common::AtomicCompareAndSwap(time_point.pack.data(), new_time_point.pack,
current_time_point.pack));
/// The clock cannot be more precise than the guest timer, remove the lower bits
return accumulated_ticks & inaccuracy_mask;
return new_time_point.inner.accumulated_ticks & inaccuracy_mask;
}
void NativeClock::Pause(bool is_paused) {
if (!is_paused) {
_mm_mfence();
last_measure = __rdtsc();
TimePoint current_time_point{};
TimePoint new_time_point{};
do {
current_time_point.pack = time_point.pack;
new_time_point.pack = current_time_point.pack;
_mm_mfence();
new_time_point.inner.last_measure = __rdtsc();
} while (!Common::AtomicCompareAndSwap(time_point.pack.data(), new_time_point.pack,
current_time_point.pack));
}
}

22
src/common/x64/native_clock.h
View file

@ -6,7 +6,6 @@
#include <optional>
#include "common/spin_lock.h"
#include "common/wall_clock.h"
namespace Common {
@ -32,22 +31,29 @@ public:
private:
u64 GetRTSC();
union alignas(16) TimePoint {
TimePoint() : pack{} {}
u128 pack{};
struct Inner {
u64 last_measure{};
u64 accumulated_ticks{};
} inner;
};
/// value used to reduce the native clocks accuracy as some apss rely on
/// undefined behavior where the level of accuracy in the clock shouldn't
/// be higher.
static constexpr u64 inaccuracy_mask = ~(UINT64_C(0x400) - 1);
SpinLock rtsc_serialize{};
u64 last_measure{};
u64 accumulated_ticks{};
u64 rtsc_frequency;
TimePoint time_point;
// factors
u64 clock_rtsc_factor{};
u64 cpu_rtsc_factor{};
u64 ns_rtsc_factor{};
u64 us_rtsc_factor{};
u64 ms_rtsc_factor{};
u64 clock_rtsc_factor{};
u64 cpu_rtsc_factor{};
u64 rtsc_frequency;
};
} // namespace X64