14.2. Required Parameters for Red Hat Enterprise Linux Guests
14.2. Required Parameters for Red Hat Enterprise Linux Guests For certain Red Hat Enterprise Linux guest 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 guest virtual machine. The table below lists versions of Red Hat Enterprise Linux and the parameters required on the specified systems. Table 14.1. Kernel parameter requirements Red Hat Enterprise Linux version Additional guest kernel parameters 7.0 and later on AMD64 and Intel 64 systems with kvm-clock Additional parameters are not required 6.1 and later on AMD64 and Intel 64 systems with kvm-clock Additional parameters are not required 6.0 on AMD64 and Intel 64 systems with kvm-clock Additional parameters are not required 6.0 on AMD64 and Intel 64 systems without kvm-clock notsc lpj= n 5.5 AMD64/Intel 64 with kvm-clock Additional parameters are not required 5.5 AMD64 and Intel 64 systems without kvm-clock notsc lpj= n 5.5 on 32-bit AMD and Intel systems with kvm-clock Additional parameters are not required 5.5 on 32-bit AMD and Intel systems without kvm-clock clocksource=acpi_pm lpj= n 5.4 on AMD64 and Intel 64 systems notsc 5.4 on 32-bit AMD and Intel systems clocksource=acpi_pm 5.3 on AMD64 and Intel 64 systems notsc 5.3 on 32-bit AMD and Intel systems clocksource=acpi_pm Note The lpj parameter requires a numeric value equal to the loops per jiffy value of the specific CPU on which the guest virtual machine runs. If you do not know this value, do not set the lpj parameter. Warning The divider kernel parameter was previously recommended for Red Hat Enterprise Linux 4 and 5 guest virtual machines that did not have high responsiveness requirements, or exist on systems with high guest density. It is no longer recommended for use with guests running Red Hat Enterprise Linux 4, or Red Hat Enterprise Linux 5 versions prior to version 5.8. divider can improve throughput on Red Hat Enterprise Linux 5 versions equal to or later than 5.8 by lowering the frequency of timer interrupts. For example, if HZ=1000 , and divider is set to 10 (that is, divider=10 ), the number of timer interrupts per period changes from the default value (1000) to 100 (the default value, 1000, divided by the divider value, 10). BZ#698842 details a bug in the way that the divider parameter interacts with interrupt and tick recording. This bug is fixed as of Red Hat Enterprise Linux 5.8. However, the divider parameter can still cause kernel panic in guests using Red Hat Enterprise Linux 4, or Red Hat Enterprise Linux 5 versions prior to version 5.8. This parameter was not implemented in Red Hat Enterprise Linux 3, so this bug does not affect Red Hat Enterprise Linux 3 guests. Red Hat Enterprise Linux 6 does not have a fixed-frequency clock interrupt; it operates in tickless mode and uses the timer dynamically as required. The divider parameter is therefore not useful for Red Hat Enterprise Linux 6, and Red Hat Enterprise Linux 6 guests are not affected by this bug.