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target-i386: Enable x2apic by default on KVM

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>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
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ehabkost authored and afaerber committed Feb 19, 2014
1 parent 8fb4f82 commit ef02ef5f4536dba090b12360a6c862ef0e57e3bc
Showing with 3 additions and 0 deletions.
  1. +1 −0 hw/i386/pc_piix.c
  2. +1 −0 hw/i386/pc_q35.c
  3. +1 −0 target-i386/cpu.c
@@ -267,6 +267,7 @@ static void pc_compat_1_7(QEMUMachineInitArgs *args)
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)
@@ -245,6 +245,7 @@ static void pc_compat_1_7(QEMUMachineInitArgs *args)
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)
@@ -369,6 +369,7 @@ static uint32_t kvm_default_features[FEATURE_WORDS] = {
(1 << KVM_FEATURE_STEAL_TIME) |
(1 << KVM_FEATURE_PV_EOI) |
(1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT),
[FEAT_1_ECX] = CPUID_EXT_X2APIC,
};

void x86_cpu_compat_disable_kvm_features(FeatureWord w, uint32_t features)

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