From: Len Brown <len.brown@xxxxxxxxx>
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.
cc: stable@xxxxxxxxxx
Acked-by: Rafael J. Wysocki <rjw@xxxxxxx>
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
---
v3: fix #define typo in header and ',' typo in printk
shorten printk to fix in 80 columns
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 43a18c7..55a11e0 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -250,6 +250,9 @@
#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_POWERSAVE 15
#define MSR_IA32_PACKAGE_THERM_STATUS 0x000001b1
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index d16c2c5..24cba78 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -448,6 +448,24 @@ 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) == ENERGY_PERF_BIAS_PERFORMANCE) {
+ printk_once(KERN_WARNING "ENERGY_PERF_BIAS:"
+ " Set to 'normal', was 'performance'\n"
+ "ENERGY_PERF_BIAS: View and update with"
+ " x86_energy_perf_policy(8)\n");
+ epb = (epb & ~0xF) | ENERGY_PERF_BIAS_NORMAL;
+ wrmsrl(MSR_IA32_ENERGY_PERF_BIAS, epb);
+ }
+ }
}
#ifdef CONFIG_X86_32
--
1.7.6.134.gcf13f
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