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  • Len Brown
     
  • MSR_IA32_ENERGY_PERF_BIAS first became available on Westmere Xeon.
    It is implemented in all Sandy Bridge processors -- mobile, desktop and server.
    It is expected to become increasingly important in subsequent generations.

    x86_energy_perf_policy is a user-space utility to set the
    hardware energy vs performance policy hint in the processor.
    Most systems would benefit from "x86_energy_perf_policy normal"
    at system startup, as the hardware default is maximum performance
    at the expense of energy efficiency.

    See x86_energy_perf_policy.8 man page for more information.

    Background:

    Linux-2.6.36 added "epb" to /proc/cpuinfo to indicate
    if an x86 processor supports MSR_IA32_ENERGY_PERF_BIAS,
    without actually modifying the MSR.

    In March, 2010, Venkatesh Pallipadi proposed a small driver
    that programmed MSR_IA32_ENERGY_PERF_BIAS, based on
    the cpufreq governor in use. It also offered
    a boot-time cmdline option to override.
    http://lkml.org/lkml/2010/3/4/457
    But hiding the hardware policy behind the
    governor choice was deemed "kinda icky".

    In June, 2010, I proposed a generic user/kernel API to
    generalize the power/performance policy trade-off.
    "RFC: /sys/power/policy_preference"
    http://lkml.org/lkml/2010/6/16/399
    That is my preference for implementing this capability,
    but I received no support on the list.

    So in September, 2010, I sent x86_energy_perf_policy.c to LKML,
    a user-space utility that scribbles directly to the MSR.
    http://lkml.org/lkml/2010/9/28/246

    Here is that same utility, after responding to some review feedback,
    to live in tools/power/, where it is easily found.

    Signed-off-by: Len Brown

    Len Brown
     
  • turbostat is a Linux tool to observe proper operation
    of Intel(R) Turbo Boost Technology.

    turbostat displays the actual processor frequency
    on x86 processors that include APERF and MPERF MSRs.

    Note that turbostat is of limited utility on Linux
    kernels 2.6.29 and older, as acpi_cpufreq cleared
    APERF/MPERF up through that release.

    On Intel Core i3/i5/i7 (Nehalem) and newer processors,
    turbostat also displays residency in idle power saving states,
    which are necessary for diagnosing any cpuidle issues
    that may have an effect on turbo-mode.

    See the turbostat.8 man page for example usage.

    Signed-off-by: Len Brown

    Len Brown