Re: [PATCH RFC v5 8/8] pvqspinlock, x86: Enable KVM to use qspinlock's PV support

[Waiman Long <waiman.long@hp.com>]

On 02/27/2014 04:31 AM, Paolo Bonzini wrote:
>   static __init int kvm_spinlock_init_jump(void)
> diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks
> index f185584..a70fdeb 100644
> --- a/kernel/Kconfig.locks
> +++ b/kernel/Kconfig.locks
> @@ -229,4 +229,4 @@ config ARCH_USE_QUEUE_SPINLOCK
>
>   config QUEUE_SPINLOCK
>   	def_bool y if ARCH_USE_QUEUE_SPINLOCK
> -	depends on SMP&&  !PARAVIRT_SPINLOCKS
> +	depends on SMP&&  (!PARAVIRT_SPINLOCKS || !XEN)
>
> Should this rather be
>
>      def_bool y if ARCH_USE_QUEUE_SPINLOCK&&  (!PARAVIRT_SPINLOCKS || !XEN)
>
> ?
>
> PARAVIRT_SPINLOCKS + XEN + QUEUE_SPINLOCK + PARAVIRT_UNFAIR_LOCKS is a
> valid combination, but it's impossible to choose PARAVIRT_UNFAIR_LOCKS
> if QUEUE_SPINLOCK is unavailable.
>
> Paolo

The PV ticketlock code assumes the presence of ticket spinlock. So it 
will cause compilation error if QUEUE_SPINLOCK is enabled. My patches 
7/8 modified the KVM code so that the PV ticketlock code can coexist 
with queue spinlock. As I haven't figure out the proper way to modify 
the Xen code, I need to disable the queue spinlock code if 
PARAVIRT_SPINLOCKS and XEN are both enabled. However, by disabling 
PARAVIRT_SPINLOCKS, we can use PARAVIRT_UNFAIR_LOCKS with XEN.

-Longman