tools: create power/x86/x86_energy_perf_policy

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@intel.com>

tools/power/x86/x86_energy_perf_policy/Makefile

@@ -0,0 +1,8 @@
+x86_energy_perf_policy : x86_energy_perf_policy.c
+
+clean :
+	rm -f x86_energy_perf_policy
+
+install :
+	install x86_energy_perf_policy /usr/bin/
+	install x86_energy_perf_policy.8 /usr/share/man/man8/

tools/power/x86/x86_energy_perf_policy/x86_energy_perf_policy.8

@@ -0,0 +1,104 @@
+.\"  This page Copyright (C) 2010 Len Brown <len.brown@intel.com>
+.\"  Distributed under the GPL, Copyleft 1994.
+.TH X86_ENERGY_PERF_POLICY 8
+.SH NAME
+x86_energy_perf_policy \- read or write MSR_IA32_ENERGY_PERF_BIAS
+.SH SYNOPSIS
+.ft B
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB "\-r"
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB 'performance'
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB 'normal'
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB 'powersave'
+.br
+.B x86_energy_perf_policy
+.RB [ "\-c cpu" ]
+.RB [ "\-v" ]
+.RB n
+.br
+.SH DESCRIPTION
+\fBx86_energy_perf_policy\fP
+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.
+
+.SS Options
+\fB-c\fP 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.
+.PP
+\fB-v\fP increases verbosity.  By default
+x86_energy_perf_policy is silent.
+.PP
+\fB-r\fP is for "read-only" mode - the unchanged state
+is read and displayed.
+.PP
+.I 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.
+.PP
+.I 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.
+.PP
+.I powersave
+Set a policy where the processor can accept
+a measurable performance hit to maximize energy efficiency.
+.PP
+.I 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.
+
+.SH NOTES
+.B "x86_energy_perf_policy "
+runs only as root.
+.SH FILES
+.ta
+.nf
+/dev/cpu/*/msr
+.fi
+
+.SH "SEE ALSO"
+msr(4)
+.PP
+.SH AUTHORS
+.nf
+Written by Len Brown <len.brown@intel.com>