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X86_ENERGY_PERF_POLICY(8)                      System Manager's Manual                      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  tol‐
       erate  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  effi‐
       ciency.

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


NOTES
       x86_energy_perf_policy runs only as root.

FILES
       /dev/cpu/*/msr