This is a note to let you know that I've just added the patch titled
x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-intel-power-initialize-msr_ia32_energy_perf_bias.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From abe48b108247e9b90b4c6739662a2e5c765ed114 Mon Sep 17 00:00:00 2001
From: Len Brown <[email protected]>
Date: Thu, 14 Jul 2011 00:53:24 -0400
Subject: x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS
From: Len Brown <[email protected]>
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 <[email protected]>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1107140051020.18606@x980
Acked-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: H. Peter Anvin <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/include/asm/msr-index.h | 3 +++
arch/x86/kernel/cpu/intel.c | 18 ++++++++++++++++++
2 files changed, 21 insertions(+)
--- 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 ENERGY_PERF_BIAS_PERFORMANCE 0
+#define ENERGY_PERF_BIAS_NORMAL 6
+#define ENERGY_PERF_BIAS_POWERSWAVE 15
#define MSR_IA32_PACKAGE_THERM_STATUS 0x000001b1
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -456,6 +456,24 @@ static void __cpuinit init_intel(struct
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
Patches currently in stable-queue which might be from [email protected] are
queue-3.0/x86-intel-power-initialize-msr_ia32_energy_perf_bias.patch
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