Citrix Hypervisor controls each processor core's frequency by adjusting the P-state.Ĭitrix recommends configuring the BIOS frequency scaling settings to use "OS control" mode (or equivalent) and to enable Turbo mode. Furthermore, some states might not be individually addressable with "xenpm set-max-cstate " and setting the maximum C-state to X does not necessarily mean that only C0.CX will be used.įrequency scaling and Turbo mode are controlled by the BIOS settings. This means that ACPI C0 will appear as C0, ACPI C1 will appear as C1, ACPI C1E will appear as C2, and so on. The C-states mentioned in the output of "xenpm get-cpuidle-states" are simply a numerical list of all the C-states that Xen knows about, listed as C0, C1, C2, etc. When setting a maximum C-state, note that C-state numbers do not necessarily correspond directly with ACPI C-state names.
Note that forcing the processor to stay in C0 will significantly increase the power consumption and may reduce the lifespan of the processor (From Section 4.2.2 of the 4th Generation Intel Core Datasheet Volume 1: "Long term reliability cannot be assured unless all the Low-Power Idle States are enabled"). Or, to make this change persist across reboots, use the following command and reboot: /opt/xensource/libexec/xen-cmdline -set-xen max_cstate=0 To immediately force the processor to stay in C0, execute the following command in dom0: xenpm set-max-cstate 0 The maximum C-state can be set as in previous versions of XenServer (6.2 and earlier). In practice, this can normally be achieved by forcing the processor to stay in C0. Some users might wish to avoid using Turbo mode, for example when running workloads that require low-latency wakeups, or when desiring consistent rather than maximal performance. Model name : Intel(R) Core(TM) i7-3770 CPU 3.40GHz To verify that Turbo mode is being used stress the CPU in a VM and check that the CPU frequency is higher than the rated value: To determine whether Turbo mode is enabled, use the following command in dom0: Hence the default configuration that uses all available C-states should give the best performance for processors supporting a Turbo mode.įor maximum performance, it is recommended that Turbo mode is enabled in the BIOS. 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
#What is turbo boost power max how to
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:
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