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

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/02/2014 16:14, Waiman Long ha scritto:
> This patch enables KVM to use the queue spinlock's PV support code
> when the PARAVIRT_SPINLOCKS kernel config option is set. However,
> PV support for Xen is not ready yet and so the queue spinlock will
> still have to be disabled when PARAVIRT_SPINLOCKS config option is
> on with Xen.
> 
> Signed-off-by: Waiman Long <Waiman.Long@hp.com>
> ---
>  arch/x86/kernel/kvm.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++
>  kernel/Kconfig.locks  |    2 +-
>  2 files changed, 55 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index f318e78..3ddc436 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -568,6 +568,7 @@ static void kvm_kick_cpu(int cpu)
>  	kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
>  }
>  
> +#ifndef CONFIG_QUEUE_SPINLOCK
>  enum kvm_contention_stat {
>  	TAKEN_SLOW,
>  	TAKEN_SLOW_PICKUP,
> @@ -795,6 +796,55 @@ static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
>  		}
>  	}
>  }
> +#else /* !CONFIG_QUEUE_SPINLOCK */
> +
> +#ifdef CONFIG_KVM_DEBUG_FS
> +static struct dentry *d_spin_debug;
> +static struct dentry *d_kvm_debug;
> +static u32 lh_kick_stats;	/* Lock holder kick count */
> +static u32 qh_kick_stats;	/* Queue head kick count  */
> +static u32 nn_kick_stats;	/* Next node kick count   */
> +
> +static int __init kvm_spinlock_debugfs(void)
> +{
> +	d_kvm_debug = debugfs_create_dir("kvm-guest", NULL);
> +	if (!d_kvm_debug) {
> +		printk(KERN_WARNING
> +		       "Could not create 'kvm' debugfs directory\n");
> +		return -ENOMEM;
> +	}
> +	d_spin_debug = debugfs_create_dir("spinlocks", d_kvm_debug);
> +
> +	debugfs_create_u32("lh_kick_stats", 0644, d_spin_debug, &lh_kick_stats);
> +	debugfs_create_u32("qh_kick_stats", 0644, d_spin_debug, &qh_kick_stats);
> +	debugfs_create_u32("nn_kick_stats", 0644, d_spin_debug, &nn_kick_stats);
> +
> +	return 0;
> +}
> +
> +static inline void inc_kick_stats(enum pv_kick_type type)
> +{
> +	if (type == PV_KICK_LOCK_HOLDER)
> +		add_smp(&lh_kick_stats, 1);
> +	else if (type == PV_KICK_QUEUE_HEAD)
> +		add_smp(&qh_kick_stats, 1);
> +	else
> +		add_smp(&nn_kick_stats, 1);
> +}
> +fs_initcall(kvm_spinlock_debugfs);
> +
> +#else /* CONFIG_KVM_DEBUG_FS */
> +static inline void inc_kick_stats(enum pv_kick_type type)
> +{
> +}
> +#endif /* CONFIG_KVM_DEBUG_FS */
> +
> +static void kvm_kick_cpu_type(int cpu, enum pv_kick_type type)
> +{
> +	kvm_kick_cpu(cpu);
> +	inc_kick_stats(type);
> +}
> +#endif /* !CONFIG_QUEUE_SPINLOCK */
>  
>  /*
>   * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
> @@ -807,8 +857,12 @@ void __init kvm_spinlock_init(void)
>  	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
>  		return;
>  
> +#ifdef CONFIG_QUEUE_SPINLOCK
> +	pv_lock_ops.kick_cpu = kvm_kick_cpu_type;
> +#else
>  	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
>  	pv_lock_ops.unlock_kick = kvm_unlock_kick;
> +#endif
>  }
>  
>  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