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.
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.
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.
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.
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 <firstname.lastname@example.org>