Using all the available C-states gives the processor most thermal headroom to enter Turbo mode. To go back to the default configuration, use the following and reboot: /opt/xensource/libexec/xen-cmdline -delete-xen mwait-idle This is not a recommended configuration as it is likely to lead to reduced performance. After this, controlling C-states in the BIOS will have an effect on Citrix Hypervisor. To revert to the C-state configuration for Intel processors that was used by older versions of XenServer (6.2 and earlier), use the following command in dom0: /opt/xensource/libexec/xen-cmdline -set-xen mwait-idle=falseĪ reboot is required for this change to take effect.

Modern CPUs can transition between C-states very quickly so the use of deep C-states has minimal performance impact but provides great potential for power saving.įalling back to use of BIOS C-state settings For example, C1 and C1E are treated as two separate states which gives Xen more flexibility in the choice of C-state. This improves performance because Xen can make more accurate decisions about which C-state to use. It chooses the correct information at boot based on the processor used. Xen Project Hypervisor comes preloaded with the C-states and performance characteristics of each processor family (like Sandy Bridge, Haswell, etc).

For AMD processors, changing C-state settings in the BIOS does have an effect for AMD processors.Ĭitrix Hypervisor uses Xen Project Hypervisor's means of enumerating and using C-states for newer Intel processors.

For Intel processors, Citrix Hypervisor uses all the available C-states regardless of the BIOS C-state settings.

It is recommended to use Citrix Hypervisor's default configuration and to enable OS-controlled frequency scaling and Turbo mode in the BIOS. Use the more power-friendly 'ondemand' CPU frequency governor

Use the BIOS settings to know which C-states are supported Use frequency scaling and Turbo mode as controlled by the BIOS settings Use the 'performance' CPU frequency governor Use all available C-states regardless of BIOS settings

This article explains how to handle your power settings and how you can change the configuration to fit your specific needs.Ĭitrix Hypervisor (formerly XenServer) has the following power settings:

The best options for quick cpu