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TSC calibration improvements

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Bind main thread to a single core for calibration.
Issue RDTSC after clock probing, may improve accuracy.
This commit is contained in:
Nekotekina 2020-04-28 21:52:37 +03:00
parent 76294beae1
commit d66bdf1653
1 changed files with 21 additions and 9 deletions
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30
Utilities/sysinfo.cpp
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@ -2,6 +2,7 @@
#include "StrFmt.h"
#include "File.h"
#include "Emu/system_config.h"
#include "Thread.h"
#ifdef _WIN32
#include "windows.h"
@ -283,37 +284,48 @@ ullong utils::get_tsc_freq()
return round_tsc(freq.QuadPart * 1024);
const ullong timer_freq = freq.QuadPart;
Sleep(1);
#else
const ullong timer_freq = 1'000'000'000;
ullong sec_base = 0;
usleep(200);
#endif
// Calibrate TSC
constexpr int samples = 40;
ullong rdtsc_data[samples];
ullong timer_data[samples];
ullong error_data[samples];
// Narrow thread affinity to a single core
const u64 old_aff = thread_ctrl::get_thread_affinity_mask();
thread_ctrl::set_thread_affinity_mask(old_aff & (0 - old_aff));
#ifndef _WIN32
struct timespec ts0;
clock_gettime(CLOCK_MONOTONIC, &ts0);
ullong sec_base = ts0.tv_sec;
#endif
for (int i = 0; i < samples; i++)
{
rdtsc_data[i] = (_mm_lfence(), __rdtsc());
#ifdef _WIN32
Sleep(1);
error_data[i] = (_mm_lfence(), __rdtsc());
LARGE_INTEGER ctr;
QueryPerformanceCounter(&ctr);
rdtsc_data[i] = (_mm_lfence(), __rdtsc());
timer_data[i] = ctr.QuadPart;
Sleep(1);
#else
usleep(200);
error_data[i] = (_mm_lfence(), __rdtsc());
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
if (i == 0)
sec_base = ts.tv_sec;
rdtsc_data[i] = (_mm_lfence(), __rdtsc());
timer_data[i] = ts.tv_nsec + (ts.tv_sec - sec_base) * 1'000'000'000;
usleep(200);
#endif
}
// Restore main thread affinity
thread_ctrl::set_thread_affinity_mask(old_aff);
// Compute average TSC
ullong acc = 0;
for (int i = 0; i < samples - 1; i++)