Re: [Qemu-devel] [PATCH 3/3] target-i386: Enable x2apic by default on KVM

["Andreas Färber" <afaerber@suse.de>]

Am 19.02.2014 15:58, schrieb Eduardo Habkost:
> When on KVM mode, enable x2apic by default on all CPU models.
> 
> Normally we try to keep the CPU model definitions as close as the real
> CPUs as possible, but x2apic can be emulated by KVM without host CPU
> support for x2apic, and it improves performance by reducing APIC access
> overhead. x2apic emulation is available on KVM since 2009 (Linux
> 2.6.32-rc1), there's no reason for not enabling x2apic by default when
> running KVM.
> 
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
> ---
>  hw/i386/pc_piix.c | 1 +
>  hw/i386/pc_q35.c  | 2 ++
>  target-i386/cpu.c | 1 +
>  3 files changed, 4 insertions(+)
> 
> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> index dab0c78..cf12873 100644
> --- a/hw/i386/pc_piix.c
> +++ b/hw/i386/pc_piix.c
> @@ -260,6 +260,7 @@ static void pc_compat_1_7(QEMUMachineInitArgs *args)
>  {
>      smbios_type1_defaults = false;
>      gigabyte_align = false;
> +    x86_cpu_compat_disable_kvm_features(FEAT_1_ECX, CPUID_EXT_X2APIC);
>  }
>  
>  static void pc_compat_1_6(QEMUMachineInitArgs *args)
> diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> index a7f6260..71b05f1 100644
> --- a/hw/i386/pc_q35.c
> +++ b/hw/i386/pc_q35.c
> @@ -244,6 +244,8 @@ static void pc_compat_1_7(QEMUMachineInitArgs *args)
>  {
>      smbios_type1_defaults = false;
>      gigabyte_align = false;
> +    x86_cpu_compat_disable_kvm_features(FEAT_1_ECX, CPUID_EXT_X2APIC);
> +
>  }
>  
>  static void pc_compat_1_6(QEMUMachineInitArgs *args)
[snip]

Needed rebase:

diff --cc hw/i386/pc_piix.c
index 5011c3a,ebd442e..0000000
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@@ -266,7 -266,7 +266,8 @@@ static void pc_compat_1_7(QEMUMachineIn
  {
      smbios_type1_defaults = false;
      gigabyte_align = false;
 +    option_rom_has_mr = true;
+     x86_cpu_compat_disable_kvm_features(FEAT_1_ECX, CPUID_EXT_X2APIC);
  }

  static void pc_compat_1_6(QEMUMachineInitArgs *args)
diff --cc hw/i386/pc_q35.c
index 4b0456a,71b05f1..0000000
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@@ -244,7 -244,8 +244,8 @@@ static void pc_compat_1_7(QEMUMachineIn
  {
      smbios_type1_defaults = false;
      gigabyte_align = false;
 +    option_rom_has_mr = true;
+     x86_cpu_compat_disable_kvm_features(FEAT_1_ECX, CPUID_EXT_X2APIC);
 -
  }

  static void pc_compat_1_6(QEMUMachineInitArgs *args)

Andreas

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