void CCPUFrequencyMonitor::StartThreads()
{
UIETWASSERT(!hExitEvent_);
if (!hExitEvent_)
{
// Must do all this before creating the child threads.
SYSTEM_INFO systemInfo;
GetSystemInfo(&systemInfo);
numCPUs_ = systemInfo.dwNumberOfProcessors;
// Clamp to the number of processors that can be identified by
// SetThreadAffinityMask - 32 or 64.
if (numCPUs_ > sizeof(DWORD_PTR) * 8)
numCPUs_ = sizeof(DWORD_PTR) * 8;
threads_.resize(numCPUs_);
quit_ = false;
workStartSemaphore_ = CreateSemaphore(nullptr, 0, numCPUs_, nullptr);
resultsDoneSemaphore_ = CreateSemaphore(nullptr, 0, numCPUs_, nullptr);
if (!workStartSemaphore_ || !resultsDoneSemaphore_)
return;
// Create numCPUs_ threads, set their affinity to individual CPU
// cores, and raise their priority. This will mostly ensure that they
// run promptly and on the desired CPU core.
for (unsigned i = 0; i < numCPUs_; ++i)
{
threads_[i].pOwner = this;
threads_[i].cpuNumber = i;
HANDLE hThread = CreateThread(nullptr, 0x10000, StaticPerCPUSamplingThread, &threads_[i], 0, nullptr);
if (hThread)
{
SetThreadAffinityMask(hThread, DWORD_PTR(1) << i);
SetThreadPriority(hThread, THREAD_PRIORITY_HIGHEST);
}
threads_[i].hThread = hThread;
}
// Get the initial frequency
QPCElapsedTimer timer;
// Run the test long enough so that the OS will ramp up the CPU to
// full speed.
startFrequency_ = MeasureFrequency(600);
float testElapsed = static_cast<float>(timer.ElapsedSeconds());
ETWMark2F("Startup CPU frequency (MHz) and measurement time (s)", startFrequency_, testElapsed);
// Once the monitor thread is created the other threads will start
// being told to do measurements occasionally.
hExitEvent_ = CreateEvent(nullptr, FALSE, FALSE, nullptr);
hThread_ = CreateThread(NULL, 0, StaticMonitorThread, this, 0, NULL);
}
}
void CCPUFrequencyMonitor::PerCPUSamplingThread(int cpuNumber)
{
for (;;)
{
// Wait until its time to measure the CPU frequency.
WaitForSingleObject(workStartSemaphore_, INFINITE);
if (quit_)
break;
float frequency = MeasureFrequency(kRetryCount);
threads_[cpuNumber].frequency = frequency;
ReleaseSemaphore(resultsDoneSemaphore_, 1, nullptr);
}
}
