On Thursday, July 14, 2011, Len Brown wrote:
> 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
> Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Acked-by: Rafael J. Wysocki <rjw@xxxxxxx>
> ---
> 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..91fedd9 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_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
> index d16c2c5..7c1ca07 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) == 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
>
_______________________________________________
linux-pm mailing list
linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linux-foundation.org/mailman/listinfo/linux-pm
