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>

                                                                        X86_ENERGY_PERF_POLICY(8)