How can I have a fast and high resolution timer on Windows? - windows

Question

I'm writing a profiler that queries a timer whenever a function enters or exits. So it's possible that it's queried thousands of times a second.
Initially I used QueryPerformanceCounter, despite the fact it's high resolution, it turned out to be quite slow. According to What happens when QueryPerformanceCounter is called? question I also got a noticeable slowdown when I use QPC in the profiler, but probably not that bad 1-2ms figure. If I replace it with GetTickCount I don't notice any slowdown, but that function is inaccurate for the profiling.
The mentioned question mention affinity masks. I tried to use SetProcessAffinityMask(GetCurrentProcess(), 1) to bind it but it doesn't improve the performance at all.
I don't know whether it matters or not, but so far I tested it on Windows that runs in VirtualBox on a Linux host. Could it be the problem?

Answer 1

The highest resolution timers I'm aware of on Windows are the multimedia timers available via winmm.dll
Here's a class I've had lying around for my own perf testing needs - give 'er a whirl:
public class HighResTimer
{
private delegate void TimerEventHandler(int id, int msg, IntPtr user, int dw1, int dw2);
private const int TIME_PERIODIC = 1;
private const int EVENT_TYPE = TIME_PERIODIC;
[System.Runtime.InteropServices.DllImport("winmm.dll")]
private static extern int timeSetEvent( int delay, int resolution, TimerEventHandler handler, IntPtr user, int eventType);
[System.Runtime.InteropServices.DllImport("winmm.dll")]
private static extern int timeKillEvent(int id);
[System.Runtime.InteropServices.DllImport("winmm.dll")]
private static extern int timeBeginPeriod(int msec);
[System.Runtime.InteropServices.DllImport("winmm.dll")]
private static extern int timeEndPeriod(int msec);
private int _timerId;
private TimerEventHandler _handler = delegate {};
public event EventHandler OnTick;
public HighResTimer(int delayInMs)
{
timeBeginPeriod(1);
_handler = new TimerEventHandler(timerElapsed);
_timerId = timeSetEvent(delayInMs, 0, _handler, IntPtr.Zero, EVENT_TYPE);
}
public void Stop()
{
int res = timeKillEvent(_timerId);
timeEndPeriod(1);
_timerId = 0;
}
private void timerElapsed(int id, int msg, IntPtr user, int dw1, int dw2)
{
OnTick(this, new EventArgs());
}
}

Answer 2

Ended up using the RDTSC instruction directly. So I wrote a wrapper for it in GCC:
static inline unsigned long long rdtsc(void)
{
unsigned hi, lo;
asm volatile ("rdtsc" : "=a"(lo), "=d"(hi));
return ( (unsigned long long)lo)|( ((unsigned long long)hi)<<32 );
}
No slowdowns and apparently have quite higher resolution than QueryPerformanceCounter.
The code based on this answer.