• Srinivas Pandruvada's avatar
    cpufreq: intel_pstate: Disable energy efficiency optimization · a6b1dc61
    Srinivas Pandruvada authored
    commit 6e978b22 upstream.
    
    Some Kabylake desktop processors may not reach max turbo when running in
    HWP mode, even if running under sustained 100% utilization.
    
    This occurs when the HWP.EPP (Energy Performance Preference) is set to
    "balance_power" (0x80) -- the default on most systems.
    
    It occurs because the platform BIOS may erroneously enable an
    energy-efficiency setting -- MSR_IA32_POWER_CTL BIT-EE, which is not
    recommended to be enabled on this SKU.
    
    On the failing systems, this BIOS issue was not discovered when the
    desktop motherboard was tested with Windows, because the BIOS also
    neglects to provide the ACPI/CPPC table, that Windows requires to enable
    HWP, and so Windows runs in legacy P-state mode, where this setting has
    no effect.
    
    Linux' intel_pstate driver does not require ACPI/CPPC to enable HWP, and
    so it runs in HWP mode, exposing this incorrect BIOS configuration.
    
    There are several ways to address this problem.
    
    First, Linux can also run in legacy P-state mode on this system.
    As intel_pstate is how Linux enables HWP, booting with
    "intel_pstate=disable"
    will run in acpi-cpufreq/ondemand legacy p-state mode.
    
    Or second, the "performance" governor can be used with intel_pstate,
    which will modify HWP.EPP to 0.
    
    Or third, starting in 4.10, the
    /sys/devices/system/cpu/cpufreq/policy*/energy_performance_preference
    attribute in can be updated from "balance_power" to "performance".
    
    Or fourth, apply this patch, which fixes the erroneous setting of
    MSR_IA32_POWER_CTL BIT_EE on this model, allowing the default
    configuration to function as designed.
    Signed-off-by: default avatarSrinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
    Reviewed-by: default avatarLen Brown <len.brown@intel.com>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    a6b1dc61
intel_pstate.c 48.9 KB