Re: [PATCH]ACPI: re-enable mwait for xen cpuidle

[Keir Fraser <keir.fraser@eu.citrix.com>]

It also has wider impact, including questionable effect on existing dom0
kernels which have never been tested with MONITOR/MWAIT present in
virtualised CPUID. I'm not sure about making this change even in current
xen-unstable (but not dead against it), and there's no chance for 4.0 and
3.4 branches.

 -- Keir

On 02/04/2010 14:41, "Wei, Gang" <gang.wei@intel.com> wrote:

> The 3rd choice: don't clear MWAIT feature in xen. This should be the best
> choice.
> 
> Jimmy
> 
> X86: re-enable mwait for xen cpuidle
> 
> Xen hypervisor doesn't export mwait feature to dom0, but latest Linux kernel
> start to check this feature while initializing _PDC object. Pass the MWAIT
> feature to dom0 to let dom0 got & pass to xen correct C state info.
> 
> Signed-off-by: Wei Gang <gang.wei@intel.com>
> 
> diff -r 537451477469 xen/arch/x86/traps.c
> --- a/xen/arch/x86/traps.c Thu Apr 01 09:55:27 2010 +0100
> +++ b/xen/arch/x86/traps.c Sat Apr 03 05:26:53 2010 +0800
> @@ -776,7 +776,6 @@ static void pv_cpuid(struct cpu_user_reg
>          __clear_bit(X86_FEATURE_PBE, &d);
>  
>          __clear_bit(X86_FEATURE_DTES64 % 32, &c);
> -        __clear_bit(X86_FEATURE_MWAIT % 32, &c);
>          __clear_bit(X86_FEATURE_DSCPL % 32, &c);
>          __clear_bit(X86_FEATURE_VMXE % 32, &c);
>          __clear_bit(X86_FEATURE_SMXE % 32, &c);
> @@ -814,7 +813,6 @@ static void pv_cpuid(struct cpu_user_reg
>          __clear_bit(X86_FEATURE_SKINIT % 32, &c);
>          __clear_bit(X86_FEATURE_WDT % 32, &c);
>          break;
> -    case 5: /* MONITOR/MWAIT */
>      case 0xa: /* Architectural Performance Monitor Features */
>      case 0x8000000a: /* SVM revision and features */
>      case 0x8000001b: /* Instruction Based Sampling */