Re: [Xen-devel] [PATCH RFC v5 5/8] pvqspinlock, x86: Enable unfair queue spinlock in a KVM guest

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Feb 26, 2014 at 10:14:25AM -0500, Waiman Long wrote:
> This patch adds a KVM init function to activate the unfair queue
> spinlock in a KVM guest when the PARAVIRT_UNFAIR_LOCKS kernel config
> option is selected.
> 
> Signed-off-by: Waiman Long <Waiman.Long@xxxxxx>
> ---
>  arch/x86/kernel/kvm.c |   17 +++++++++++++++++
>  1 files changed, 17 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 713f1b3..a489140 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -826,3 +826,20 @@ static __init int kvm_spinlock_init_jump(void)
>  early_initcall(kvm_spinlock_init_jump);
>  
>  #endif       /* CONFIG_PARAVIRT_SPINLOCKS */
> +
> +#ifdef CONFIG_PARAVIRT_UNFAIR_LOCKS
> +/*
> + * Enable unfair lock if running in a real para-virtualized environment
> + */
> +static __init int kvm_unfair_locks_init_jump(void)
> +{
> +     if (!kvm_para_available())
> +             return 0;

I think you also need to check for !kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)?
Otherwise you might enable this, but the kicker function won't be
enabled.
> +
> +     static_key_slow_inc(&paravirt_unfairlocks_enabled);
> +     printk(KERN_INFO "KVM setup unfair spinlock\n");
> +
> +     return 0;
> +}
> +early_initcall(kvm_unfair_locks_init_jump);
> +#endif
> -- 
> 1.7.1
> 

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