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)