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Old 07-14-2011, 04:53 AM
Len Brown
Default x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS

BugLink: http://bugs.launchpad.net/bugs/760131

commit abe48b108247e9b90b4c6739662a2e5c765ed114 upstream.

Since 2.6.36 (23016bf0d25), Linux prints the existence of "epb" in /proc/cpuinfo,
Since 2.6.38 (d5532ee7b40), the x86_energy_perf_policy(8) utility has
been available in-tree to update MSR_IA32_ENERGY_PERF_BIAS.

However, the typical BIOS fails to initialize the MSR, presumably
because this is handled by high-volume shrink-wrap operating systems...

Linux distros, on the other hand, do not yet invoke x86_energy_perf_policy(8).
As a result, WSM-EP, SNB, and later hardware from Intel will run in its
default hardware power-on state (performance), which assumes that users
care for performance at all costs and not for energy efficiency.
While that is fine for performance benchmarks, the hardware's intended default
operating point is "normal" mode...

Initialize the MSR to the "normal" by default during kernel boot.

x86_energy_perf_policy(8) is available to change the default after boot,
should the user have a different preference.

Signed-off-by: Len Brown <len.brown@intel.com>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1107140051020.18606@x980
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
arch/x86/include/asm/msr-index.h | 3 +++
arch/x86/kernel/cpu/intel.c | 18 ++++++++++++++++++
2 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 485b4f1..23a9d89 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -259,6 +259,9 @@
#define MSR_IA32_TEMPERATURE_TARGET 0x000001a2

#define MSR_IA32_ENERGY_PERF_BIAS 0x000001b0

#define MSR_IA32_PACKAGE_THERM_STATUS 0x000001b1

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 1edf5ba..da0d779 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -456,6 +456,24 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)

if (cpu_has(c, X86_FEATURE_VMX))
+ /*
+ * Initialize MSR_IA32_ENERGY_PERF_BIAS if BIOS did not.
+ * x86_energy_perf_policy(8) is available to change it at run-time
+ */
+ if (cpu_has(c, X86_FEATURE_EPB)) {
+ u64 epb;
+ rdmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+ if ((epb & 0xF) == 0) {
+ printk_once(KERN_WARNING, "x86: updated energy_perf_bias"
+ " to 'normal' from 'performance'
+ "You can view and update epb via utility,"
+ " such as x86_energy_perf_policy(8)
+ epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL;
+ wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+ }
+ }

#ifdef CONFIG_X86_32

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