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measure_interval.cpp
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measure_interval.cpp
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/*
Copyright 2020 Cygnus Software. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
/*
This program monitors the effects of the current global timer interrupt
interval as set by timeBeginPeriod. For most interesting results run this
program while change_interval.exe is running in another window, and when
nothing else that sets the timer interrupt interval is running.
*/
#include <Windows.h>
#include <cstdint>
#include <cstdio>
#include <vcruntime.h>
NTSYSAPI NTSTATUS NTAPI NtQueryTimerResolution(PULONG MinimumResolution, PULONG MaximumResolution, PULONG CurrentResolution);
// Returns the current timer resolution in 100 ns units (10,000 implies a one ms timer interval).
ULONG GetTimerResolution() {
static HMODULE ntdll = LoadLibrary("ntdll.dll");
static auto QueryTimerResolution = reinterpret_cast<decltype(&::NtQueryTimerResolution)>(GetProcAddress(ntdll, "NtQueryTimerResolution"));
ULONG minimum, maximum, current;
QueryTimerResolution(&minimum, &maximum, ¤t);
return current;
}
int64_t HighPrecisionTime() {
LARGE_INTEGER time;
QueryPerformanceCounter(&time);
return time.QuadPart;
}
int64_t HighPrecisionFrequency() {
LARGE_INTEGER frequency;
QueryPerformanceFrequency(&frequency);
return frequency.QuadPart;
}
DWORD TimeGetTimeResolution() {
const DWORD time_start = timeGetTime();
// Wait for timeGetTime to return a different value.
while (time_start == timeGetTime());
return timeGetTime() - time_start;
}
void SleepTest(bool tabbed) {
const ULONG resolution_start = GetTimerResolution();
// Measure the resolution of timeGetTime()
const DWORD time_get_time_resolution = TimeGetTimeResolution();
// Measure the behavior of Sleep(1)
const DWORD start = timeGetTime();
// Lots of space to store the wakeup times.
DWORD times[2000];
times[0] = start;
int64_t times_precise[2000];
times_precise[0] = HighPrecisionTime();
int iterations = 0;
// Wait for one second to have elapsed.
constexpr DWORD kLoopLength = 1000;
while (timeGetTime() - start < kLoopLength) {
Sleep(1);
++iterations;
times[iterations] = timeGetTime();
times_precise[iterations] = HighPrecisionTime();
}
const ULONG resolution_end = GetTimerResolution();
// Only report results if the timer resolution hasn't changed during the measurement.
if (resolution_start == resolution_end) {
if (tabbed)
printf("%.1f\t%lu\t%.1f\n", resolution_start / 1e4,
time_get_time_resolution, double(kLoopLength) / iterations);
else
printf("Global timer interrupt interval is %4.1f ms. timeGetTime "
"resolution is %2lu. Delay from Sleep(1) is ~%4.1f ms.\n",
resolution_start / 1e4, time_get_time_resolution,
double(kLoopLength) / iterations);
const size_t count = 50;
int interval_counts[count] = {};
int interval_counts_precise[count] = {};
for (int i = 0; i < iterations; ++i) {
DWORD elapsed = times[i + 1] - times[i];
if (elapsed >= count)
elapsed = count - 1;
++interval_counts[elapsed];
DWORD elapsed_precise = static_cast<DWORD>(
0.5 + 1e3 * (times_precise[i + 1] - times_precise[i]) /
HighPrecisionFrequency());
if (elapsed_precise >= count)
elapsed_precise = count - 1;
++interval_counts_precise[elapsed_precise];
// Optionally print full details to see the spacing of intervals.
/*if (resolution_start == 80000) {
printf("%d\t%d\n", elapsed, elapsed_precise);
}*/
}
printf("Delay\tCount\tCountQPC\tTable of Sleep(1) length occurrences.\n");
for (size_t i = 0; i < count; ++i)
if (interval_counts[i] || interval_counts_precise[i])
printf("%2zu\t%2d\t%2d\n", i, interval_counts[i], interval_counts_precise[i]);
}
}
int main(int argc, char *argv[]) {
bool tabbed = false;
if (argc > 1 && _stricmp(argv[1], "-tabbed") == 0)
tabbed = true;
if (tabbed)
printf("Rsltion\ttmGetTm\tSleep(1)\n");
while (true) {
SleepTest(tabbed);
}
}