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native_clock: Round RDTSC frequency to the nearest 1000

This commit is contained in:
Morph 2023-03-03 21:02:24 -05:00
parent 026eaddbee
commit 376a414f5b
1 changed files with 12 additions and 5 deletions
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17
src/common/x64/native_clock.cpp
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@ -6,6 +6,7 @@
#include <thread> #include <thread>
#include "common/atomic_ops.h" #include "common/atomic_ops.h"
#include "common/steady_clock.h"
#include "common/uint128.h" #include "common/uint128.h"
#include "common/x64/native_clock.h" #include "common/x64/native_clock.h"
@ -39,6 +40,12 @@ static u64 FencedRDTSC() {
} }
#endif #endif
template <u64 Nearest>
static u64 RoundToNearest(u64 value) {
const auto mod = value % Nearest;
return mod >= (Nearest / 2) ? (value - mod + Nearest) : (value - mod);
}
u64 EstimateRDTSCFrequency() { u64 EstimateRDTSCFrequency() {
// Discard the first result measuring the rdtsc. // Discard the first result measuring the rdtsc.
FencedRDTSC(); FencedRDTSC();
@ -46,18 +53,18 @@ u64 EstimateRDTSCFrequency() {
FencedRDTSC(); FencedRDTSC();
// Get the current time. // Get the current time.
const auto start_time = std::chrono::steady_clock::now(); const auto start_time = Common::SteadyClock::Now();
const u64 tsc_start = FencedRDTSC(); const u64 tsc_start = FencedRDTSC();
// Wait for 200 milliseconds. // Wait for 250 milliseconds.
std::this_thread::sleep_for(std::chrono::milliseconds{200}); std::this_thread::sleep_for(std::chrono::milliseconds{250});
const auto end_time = std::chrono::steady_clock::now(); const auto end_time = Common::SteadyClock::Now();
const u64 tsc_end = FencedRDTSC(); const u64 tsc_end = FencedRDTSC();
// Calculate differences. // Calculate differences.
const u64 timer_diff = static_cast<u64>( const u64 timer_diff = static_cast<u64>(
std::chrono::duration_cast<std::chrono::nanoseconds>(end_time - start_time).count()); std::chrono::duration_cast<std::chrono::nanoseconds>(end_time - start_time).count());
const u64 tsc_diff = tsc_end - tsc_start; const u64 tsc_diff = tsc_end - tsc_start;
const u64 tsc_freq = MultiplyAndDivide64(tsc_diff, 1000000000ULL, timer_diff); const u64 tsc_freq = MultiplyAndDivide64(tsc_diff, 1000000000ULL, timer_diff);
return tsc_freq; return RoundToNearest<1000>(tsc_freq);
} }
namespace X64 { namespace X64 {