Re: [Qemu-devel] [PATCH v3 8/8] target-i386/kvm: cache the return value of kvm_enable_x2apic()

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 30 Sep 2016 18:10:13 +0200
Radim Krčmář <rkrcmar@redhat.com> wrote:

> Assume that KVM would have returned the same on subsequent runs.
> Abstract the memoizaiton pattern into macros.
s/memoi/memori/i
Throughout whole patch

> 
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
> ---
>  target-i386/kvm.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> index 0fd664648665..113c5bf058ba 100644
> --- a/target-i386/kvm.c
> +++ b/target-i386/kvm.c
> @@ -129,10 +129,27 @@ static bool kvm_x2apic_api_set_flags(uint64_t flags)
>      return !kvm_vm_enable_cap(s, KVM_CAP_X2APIC_API, 0, flags);
>  }
>  
> +#define MEMOIZE_RESULT(_result, _fn) \
> +    ({ \
> +        static bool _memoized; \
> +        if (_memoized) { \
> +            return _result; \
> +        } \
> +        _memoized = true; \
> +        _result = _fn; \
> +    })
> +
> +#define MEMOIZE(_fn) \
> +    ({ \
> +        static typeof(_fn) _result; \
> +        MEMOIZE_RESULT(_result, _fn); \
> +    })
> +
>  bool kvm_enable_x2apic(void)
>  {
> -    return kvm_x2apic_api_set_flags(KVM_X2APIC_API_USE_32BIT_IDS |
> -                                    KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK);
> +    return MEMOIZE(
> +             kvm_x2apic_api_set_flags(KVM_X2APIC_API_USE_32BIT_IDS |
> +                                      KVM_X2APIC_API_DISABLE_BROADCAST_QUIRK));
>  }
>  
>  static int kvm_get_tsc(CPUState *cs)