Commit abe48b10 authored Jul 14, 2011 by Len Brown Committed by H. Peter Anvin Jul 14, 2011

x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS



Since 2.6.36 (23016bf0), Linux prints the existence of "epb" in /proc/cpuinfo,
Since 2.6.38 (d5532ee7), 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>
Cc: <stable@kernel.org>

parent 620917de

arch/x86/include/asm/msr-index.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -259,6 +259,9 @@
		#define MSR_IA32_TEMPERATURE_TARGET 0x000001a2

		#define MSR_IA32_ENERGY_PERF_BIAS 0x000001b0
		#define ENERGY_PERF_BIAS_PERFORMANCE 0
		#define ENERGY_PERF_BIAS_NORMAL 6
		#define ENERGY_PERF_BIAS_POWERSWAVE 15

		#define MSR_IA32_PACKAGE_THERM_STATUS 0x000001b1

arch/x86/kernel/cpu/intel.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -456,6 +456,24 @@ static void __cpuinit init_intel(struct cpuinfo_x86 *c)

		if (cpu_has(c, X86_FEATURE_VMX))
		detect_vmx_virtcap(c);

		/*
		* 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'\n"
		"You can view and update epb via utility,"
		" such as x86_energy_perf_policy(8)\n");
		epb = (epb & ~0xF) \| ENERGY_PERF_BIAS_NORMAL;
		wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
		}
		}
		}

		#ifdef CONFIG_X86_32

Admin message