blob: 8eaaad648cdb92743e373adaacb8a16bbdc8f551 [file] [log] [blame]
.\" This page Copyright (C) 2010 Len Brown <>
.\" Distributed under the GPL, Copyleft 1994.
x86_energy_perf_policy \- read or write MSR_IA32_ENERGY_PERF_BIAS
.ft B
.B x86_energy_perf_policy
.RB [ "\-c cpu" ]
.RB [ "\-v" ]
.RB "\-r"
.B x86_energy_perf_policy
.RB [ "\-c cpu" ]
.RB [ "\-v" ]
.RB 'performance'
.B x86_energy_perf_policy
.RB [ "\-c cpu" ]
.RB [ "\-v" ]
.RB 'normal'
.B x86_energy_perf_policy
.RB [ "\-c cpu" ]
.RB [ "\-v" ]
.RB 'powersave'
.B x86_energy_perf_policy
.RB [ "\-c cpu" ]
.RB [ "\-v" ]
.RB n
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.
.SS Options
\fB-c\fP 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.
\fB-v\fP increases verbosity. By default
x86_energy_perf_policy is silent.
\fB-r\fP is for "read-only" mode - the unchanged state
is read and displayed.
.I 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.
.I 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.
.I powersave
Set a policy where the processor can accept
a measurable performance hit to maximize energy efficiency.
.I 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.
.B "x86_energy_perf_policy "
runs only as root.
Written by Len Brown <>