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native_clock: Wait for less time in EstimateRDTSCFrequency 

In my testing, waiting for 200ms provided the same level of precision as the previous implementation when estimating the RDTSC frequency.
This significantly improves the yuzu executable launch times since we reduced the wait time from 3 seconds to 200 milliseconds.
This commit is contained in:
Morph 2021-12-02 16:12:23 -05:00
parent a2fb5a13b2
commit f919498f8f
1 changed files with 18 additions and 18 deletions
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36
src/common/x64/native_clock.cpp
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@ -15,26 +15,26 @@
namespace Common {
u64 EstimateRDTSCFrequency() {
const auto milli_10 = std::chrono::milliseconds{10};
// get current time
// Discard the first result measuring the rdtsc.
_mm_mfence();
const u64 tscStart = __rdtsc();
const auto startTime = std::chrono::steady_clock::now();
// wait roughly 3 seconds
while (true) {
auto milli = std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::steady_clock::now() - startTime);
if (milli.count() >= 3000)
break;
std::this_thread::sleep_for(milli_10);
}
const auto endTime = std::chrono::steady_clock::now();
__rdtsc();
std::this_thread::sleep_for(std::chrono::milliseconds{1});
_mm_mfence();
const u64 tscEnd = __rdtsc();
// calculate difference
const u64 timer_diff =
std::chrono::duration_cast<std::chrono::nanoseconds>(endTime - startTime).count();
const u64 tsc_diff = tscEnd - tscStart;
__rdtsc();
// Get the current time.
const auto start_time = std::chrono::steady_clock::now();
_mm_mfence();
const u64 tsc_start = __rdtsc();
// 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();
// Calculate differences.
const u64 timer_diff = static_cast<u64>(
std::chrono::duration_cast<std::chrono::nanoseconds>(end_time - start_time).count());
const u64 tsc_diff = tsc_end - tsc_start;
const u64 tsc_freq = MultiplyAndDivide64(tsc_diff, 1000000000ULL, timer_diff);
return tsc_freq;
}