Re: [Xen-devel] [PATCH 3/4] paravirt: add virt_spin_lock pvops function

[Peter Zijlstra <peterz@xxxxxxxxxxxxx>]

On Tue, Sep 05, 2017 at 03:24:43PM +0200, Juergen Gross wrote:
> diff --git a/arch/x86/include/asm/qspinlock.h 
> b/arch/x86/include/asm/qspinlock.h
> index 48a706f641f2..fbd98896385c 100644
> --- a/arch/x86/include/asm/qspinlock.h
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct 
> qspinlock *lock)
>       smp_store_release((u8 *)lock, 0);
>  }
>  


Should this not have:

#ifdef CONFIG_PARAVIRT

?

> +static inline bool native_virt_spin_lock(struct qspinlock *lock)
> +{
> +     if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> +             return false;
> +
> +     /*
> +      * On hypervisors without PARAVIRT_SPINLOCKS support we fall
> +      * back to a Test-and-Set spinlock, because fair locks have
> +      * horrible lock 'holder' preemption issues.
> +      */
> +
> +     do {
> +             while (atomic_read(&lock->val) != 0)
> +                     cpu_relax();
> +     } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
> +
> +     return true;
> +}

#endif

> +
>  #ifdef CONFIG_PARAVIRT_SPINLOCKS
>  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
> val);
>  extern void __pv_init_lock_hash(void);


>  #ifdef CONFIG_PARAVIRT
>  #define virt_spin_lock virt_spin_lock
> +#ifdef CONFIG_PARAVIRT_SPINLOCKS
>  static inline bool virt_spin_lock(struct qspinlock *lock)
>  {
> +     return pv_virt_spin_lock(lock);
> +}
> +#else
> +static inline bool virt_spin_lock(struct qspinlock *lock)
> +{
> +     return native_virt_spin_lock(lock);
>  }
> +#endif /* CONFIG_PARAVIRT_SPINLOCKS */
>  #endif /* CONFIG_PARAVIRT */

Because I think the above only ever uses native_virt_spin_lock() when
PARAVIRT.

> @@ -1381,6 +1382,7 @@ void __init native_smp_prepare_boot_cpu(void)
>       /* already set me in cpu_online_mask in boot_cpu_init() */
>       cpumask_set_cpu(me, cpu_callout_mask);
>       cpu_set_state_online(me);
> +     native_pv_lock_init();
>  }

Aah, this is where that goes.. OK that works too.

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