Knowledge Base

With certain VMware products, time and processor speed in a virtual machine are affected by the power management features, because they change the speed at which the computer's processor runs. That can cause inaccuracies in clocks and timers in the virtual machine and can also cause inaccurate readings of rated processor speed.

To work around these problems, you may need to set the processor so it runs at a constant speed.

With Workstation 4.0 and GSX Server 2.5.1 and later versions, you may be able to correct the clock timing without forcing the processor to run at a constant speed; see article 1227 (for Windows hosts) at www.vmware.com/support/kb/enduser/std_adp.php?p_faqid=1227 or article 1591 (for Linux hosts) at www.vmware.com/support/kb/enduser/std_adp.php?p_faqid=1591 .

On Windows hosts: Take the following steps before you start your VMware software. The following example uses SpeedStep as an example, but the process for PowerNow or Cool'n'Quiet is similar.

1. On your Windows host system, in the Control Panel, double-click the Power Options icon. On Windows Server 2003 hosts (VMware GSX Server or Workstation) or Windows XP hosts (VMware Workstation only), you may need to click Classic View first.
2. Click the Intel SpeedStep technology tab.
3. Under Plugged in, select Maximum Performance.
4. Under Running on batteries, select Maximum Performance.
5. Click OK to close the SpeedStep dialog box.
6. Reboot the host computer. This step ensures that your VMware software correctly detects the changed speed setting.

When you are not running your VMware software, you may want to restore these settings to their previous values to extend battery life.

Note: If there is no SpeedStep tab in the Power Options control panel, you may be able to add one by installing the proper driver. Go to the Web site of your computer's manufacturer and search for "Intel SpeedStep driver," "Intel SpeedStep applet" or "Intel SpeedStep application." If this software is available, install it on your host operating system. If no driver software is available for your host computer, you may find comparable configuration options in the computer's BIOS settings. See the steps for Linux hosts below for general guidelines on changing these settings.

On Linux hosts: Set the appropriate options in the computer's BIOS. The details vary from one computer to another. The process is similar to that described in the following steps for SpeedStep:

1. Shut down and reboot your host computer.
2. While your host is rebooting, press the appropriate key to enter its BIOS setup screen.
3. Navigate to the SpeedStep settings.
4. Under Intel SpeedStep Technology, select Enabled.
5. Under Power Mode for AC, select Maximum Performance.
6. Under Power Mode for Battery, select Maximum Performance.
7. Save the BIOS settings and exit.

Also disable any known daemons that alter the CPU speed. Such daemons vary among different Linux operating systems. The most common ones are cpuspeed and cpufreqd.

For more information about SpeedStep, see Intel's Web site:
support.intel.com/support/processors/mobile/pentium4/tti002.htm (Pentium 4)
support.intel.com/support/processors/mobile/pentiumiii/ss.htm (Pentium III)

For more information about PowerNow or Cool'n'Quiet, see the AMD Web site at www.amd.com.