x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS

[ upstream commit abe48b108247e9b90b4c6739662a2e5c765ed114 ]

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>
Signed-off-by: Andi Kleen <ak@linux.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>

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 7322e874430530e700e5b25a7ac8a36cbe407c5f..692c73bdc3fe058ba7ad7db075253c8898906c6f 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -231,6 +231,11 @@
 #define THERM_INT_LOW_ENABLE           (1 << 0)
 #define THERM_INT_HIGH_ENABLE          (1 << 1)
 
+#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_THERM_STATUS          0x0000019c
 
 #define THERM_STATUS_PROCHOT           (1 << 0)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index b4389441efbbd8e791289aa936369e5e73917c18..8e82a525b80cb9f3baba96bbbb936e327e3c79b2 100644 (file)
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -450,6 +450,24 @@ 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