This page Copyright (C) 2010 Len Brown <len.brown@intel.com>
Distributed under the GPL, Copyleft 1994.
x86_energy_perf_policy - read or write MSR_IA32_ENERGY_PERF_BIAS 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

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. -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.

"x86_energy_perf_policy " runs only as root.

/dev/cpu/*/msr

msr(4)

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