cpufreq: intel_pstate: Disable energy efficiency optimization

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: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: 4.6+ <stable@vger.kernel.org> # 4.6+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

path: root/fs/autofs4/Kconfig

config AUTOFS4_FS
	tristate "Kernel automounter version 4 support (also supports v3)"
	help
	  The automounter is a tool to automatically mount remote file systems
	  on demand. This implementation is partially kernel-based to reduce
	  overhead in the already-mounted case; this is unlike the BSD
	  automounter (amd), which is a pure user space daemon.

	  To use the automounter you need the user-space tools from
	  <ftp://ftp.kernel.org/pub/linux/daemons/autofs/v4/>; you also
	  want to answer Y to "NFS file system support", below.

	  To compile this support as a module, choose M here: the module will be
	  called autofs4.  You will need to add "alias autofs autofs4" to your
	  modules configuration file.

	  If you are not a part of a fairly large, distributed network or
	  don't have a laptop which needs to dynamically reconfigure to the
	  local network, you probably do not need an automounter, and can say
	  N here.