Hi there,
I am using a Ubuntu 12.04 x64 host to run a Windows 2008 RC2 guest and
I have noticed very puzzling behaviour inside the guest when invoking
QueryPerformanceCounter. Specifically the program below will
periodically show a 43 second offset between loop iterations despite
the fact that loop is roughly running once per second (printing out
the guest system clock confirms this). The same thing happens on a
Windows 7 guest. The 43 second number is remarkably stable across
hosts and guests.
#include "stdafx.h"
#include "windows.h"
#include <iostream>
int main(int argc, char ** argv)
{
LARGE_INTEGER qpcnt;
QueryPerformanceCounter(&qpcnt);
auto then = qpcnt.QuadPart;
while (true) {
LARGE_INTEGER qpfreq;
QueryPerformanceFrequency(&qpfreq);
auto freq = qpfreq.QuadPart;
QueryPerformanceCounter(&qpcnt);
auto now = qpcnt.QuadPart;
auto delta_seconds = (now - then) / freq;
std::cout << delta_seconds << std::endl;
QueryPerformanceCounter(&qpcnt);
then = qpcnt.QuadPart;
Sleep (1000);
}
}
A few more details on the host:
$ uname -a
Linux think 3.2.0-48-generic #74-Ubuntu SMP Thu Jun 6 19:43:26 UTC
2013 x86_64 x86_64 x86_64 GNU/Linux
$ kvm --version
QEMU emulator version 1.0 (qemu-kvm-1.0), Copyright (c) 2003-2008
Fabrice Bellard
Any ideas on what might be happening?
Thanks in advance,
-pp
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