6.16. Other Virtual Machine Tasks

Enable SAP monitoring on a virtual machine through the Administration Portal.

Enabling SAP Monitoring on Virtual Machines

SPICE is a remote display protocol designed for virtual environments, which enables you to view a virtualized desktop or server. SPICE delivers a high quality user experience, keeps CPU consumption low, and supports high quality video streaming.

Using SPICE on a Linux machine significantly improves the movement of the mouse cursor on the console of the virtual machine. To use SPICE, the X-Windows system requires additional QXL drivers. The QXL drivers are provided with Red Hat Enterprise Linux 5.4 and later. Earlier versions are not supported. Installing SPICE on a virtual machine running Red Hat Enterprise Linux significantly improves the performance of the graphical user interface.

Virtualization poses various challenges for virtual machine time keeping. Virtual machines which use the Time Stamp Counter (TSC) as a clock source may suffer timing issues as some CPUs do not have a constant Time Stamp Counter. Virtual machines running without accurate timekeeping can have serious affects on some networked applications as your virtual machine will run faster or slower than the actual time.

KVM works around this issue by providing virtual machines with a paravirtualized clock. The KVM pvclock provides a stable source of timing for KVM guests that support it.

Presently, only Red Hat Enterprise Linux 5.4 and later virtual machines fully support the paravirtualized clock.

Virtual machines can have several problems caused by inaccurate clocks and counters:

These problems exist on other virtualization platforms and timing should always be tested.

# service ntpd start
# chkconfig ntpd on

# systemctl start ntpd.service
# systemctl enable ntpd.service

Determining if your CPU has the constant Time Stamp Counter

Your CPU has a constant Time Stamp Counter if the constant_tsc flag is present. To determine if your CPU has the constant_tsc flag run the following command:

$ cat /proc/cpuinfo | grep constant_tsc

If any output is given your CPU has the constant_tsc bit. If no output is given follow the instructions below.

Configuring hosts without a constant Time Stamp Counter

Systems without constant time stamp counters require additional configuration. Power management features interfere with accurate time keeping and must be disabled for virtual machines to accurately keep time with KVM.

If the CPU lacks the constant_tsc bit, disable all power management features (BZ#513138). Each system has several timers it uses to keep time. The TSC is not stable on the host, which is sometimes caused by cpufreq changes, deep C state, or migration to a host with a faster TSC. Deep C sleep states can stop the TSC. To prevent the kernel using deep C states append “processor.max_cstate=1” to the kernel boot options in the grub.conf file on the host:

term Red Hat Enterprise Linux Server (2.6.18-159.el5)
        root (hd0,0)
	kernel /vmlinuz-2.6.18-159.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet processor.max_cstate=1

Disable cpufreq (only necessary on hosts without the constant_tsc) by editing the /etc/sysconfig/cpuspeed configuration file and change the MIN_SPEED and MAX_SPEED variables to the highest frequency available. Valid limits can be found in the /sys/devices/system/cpu/cpu/cpufreq/scaling_available_frequencies files.

Using the engine-config tool to receive alerts when hosts drift out of sync.

You can use the engine-config tool to configure alerts when your hosts drift out of sync.

There are 2 relevant parameters for time drift on hosts: EnableHostTimeDrift and HostTimeDriftInSec. EnableHostTimeDrift, with a default value of false, can be enabled to receive alert notifications of host time drift. The HostTimeDriftInSec parameter is used to set the maximum allowable drift before alerts start being sent.

Alerts are sent once per hour per host.

Using the paravirtualized clock with Red Hat Enterprise Linux virtual machines

For certain Red Hat Enterprise Linux virtual machines, additional kernel parameters are required. These parameters can be set by appending them to the end of the /kernel line in the /boot/grub/grub.conf file of the virtual machine.

The ktune package provides an interactive Bourne shell script, fix_clock_drift.sh. When run as the superuser, this script inspects various system parameters to determine if the virtual machine on which it is run is susceptible to clock drift under load. If so, it then creates a new grub.conf.kvm file in the /boot/grub/ directory. This file contains a kernel boot line with additional kernel parameters that allow the kernel to account for and prevent significant clock drift on the KVM virtual machine. After running fix_clock_drift.sh as the superuser, and once the script has created the grub.conf.kvm file, then the virtual machine’s current grub.conf file should be backed up manually by the system administrator, the new grub.conf.kvm file should be manually inspected to ensure that it is identical to grub.conf with the exception of the additional boot line parameters, the grub.conf.kvm file should finally be renamed grub.conf, and the virtual machine should be rebooted.

The table below lists versions of Red Hat Enterprise Linux and the parameters required for virtual machines on systems without a constant Time Stamp Counter.

Trusted Platform Module (TPM) devices provide a secure crypto-processor designed to carry out cryptographic operations such as generating cryptographic keys, random numbers, and hashes, or for storing data that can be used to verify software configurations securely. TPM devices are commonly used for disk encryption.

QEMU and libvirt implement support for emulated TPM 2.0 devices, which is what Red Hat Virtualization uses to add TPM devices to Virtual Machines.

Once an emulated TPM device is added to the virtual machine, it can be used as a normal TPM 2.0 device in the guest OS.

Enabling a TPM device

Limitations

The following limitations apply: