Red Hat ENTERPRISE LINUX 5 - VIRTUALIZATION GUIDE Guide d'installation télécharger pdf (Page 134)

Chapter 14. KVM guest timing management

124

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:

title Red Hat Enterprise Linux (2.6.32-36.x86-64)

root (hd0,0)

kernel /vmlinuz-2.6.32-36.x86-64 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 para-virtualized clock with Red Hat Enterprise Linux guests

For certain Red Hat Enterprise Linux guests, 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.

The table below lists versions of Red Hat Enterprise Linux and the parameters required for guests on

systems without a constant Time Stamp Counter.

Red Hat Enterprise Linux Additional guest kernel parameters

6.0 AMD64/Intel 64 with the

para-virtualized clock

Additional parameters are not required

6.0 AMD64/Intel 64 without the

para-virtualized clock

notsc lpj=n

5.5 AMD64/Intel 64 with the

para-virtualized clock

Additional parameters are not required

5.5 AMD64/Intel 64 without the

para-virtualized clock

divider=10 notsc lpj=n

5.5 x86 with the para-virtualized

clock

Additional parameters are not required

5.5 x86 without the para-

virtualized clock

divider=10 clocksource=acpi_pm lpj=n

5.4 AMD64/Intel 64 divider=10 notsc

5.4 x86 divider=10 clocksource=acpi_pm

5.3 AMD64/Intel 64 divider=10 notsc

5.3 x86 divider=10 clocksource=acpi_pm

4.8 AMD64/Intel 64 notsc divider=10

4.8 x86 clock=pmtmr divider=10

3.9 AMD64/Intel 64 Additional parameters are not required

3.9 x86 Additional parameters are not required

https://bugzilla.redhat.com/show_bug.cgi?id=513138

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