X86_ENERGY_PERF_POLICY(8)

NAME
x86_energy_perf_policy - read or write MSR_IA32_ENERGY_PERF_BIAS

SYNOPSIS
x86_energy_perf_policy [-c cpu] [-v] -r
x86_energy_perf_policy [-c cpu] [-v] 'performance'
x86_energy_perf_policy [-c cpu] [-v] 'normal'
x86_energy_perf_policy [-c cpu] [-v] 'powersave'
x86_energy_perf_policy [-c cpu] [-v] n

DESCRIPTION
x86_energy_perf_policy allows software to convey its policy for the relative importance of performance versus energy savings to the processor.

The processor uses this information in model-specific ways when it must select trade-offs between performance and energy efficiency.

This policy hint does not supersede Processor Performance states (P-states) or CPU Idle power states (C-states), but allows software to have influence where it would otherwise be unable to express a preference.

For example, this setting may tell the hardware how aggressively or conservatively to control frequency in the "turbo range" above the explicitly OS-controlled P-state frequency range. It may also tell the hardware how aggressively is should enter the OS requested C-states.

Support for this feature is indicated by CPUID.06H.ECX.bit3 per the Intel Architectures Software Developer's Manual.

  Options
-c limits operation to a single CPU. The default is to operate on all CPUs. Note that MSR_IA32_ENERGY_PERF_BIAS is defined per logical processor, but that the initial implementations of the MSR were shared among all processors in each package.

-v increases verbosity. By default x86_energy_perf_policy is silent.

-r is for "read-only" mode - the unchanged state is read and displayed.

performance Set a policy where performance is paramount. The processor will be unwilling to sacrifice any performance for the sake of energy saving. This is the hardware default.

normal Set a policy with a normal balance between performance and energy efficiency. The processor will tolerate minor performance compromise for potentially significant energy savings. This reasonable default for most desktops and servers.

powersave Set a policy where the processor can accept a measurable performance hit to maximize energy efficiency.

n Set MSR_IA32_ENERGY_PERF_BIAS to the specified number. The range of valid numbers is 0-15, where 0 is maximum performance and 15 is maximum energy efficiency.

NOTES
x86_energy_perf_policy runs only as root.

FILES
/dev/cpu/*/msr

SEE ALSO
msr(4)

AUTHORS
Written by Len Brown <len.brown@intel.com>