x86, intel, power: Initialize MSR_IA32_ENERGY_PERF_BIAS

lenb · H. Peter Anvin · commit abe48b108247 · 2011-07-14T12:13:42.000-07:00
Since 2.6.36 (23016bf), Linux prints the existence of "epb" in /proc/cpuinfo, Since 2.6.38 (d5532ee), 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>
diff --git 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
 
diff --git 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))
 		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
