linux-kernel - Re: [PATCH 10/11] qspinlock: Paravirt support

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Date:	Wed, 18 Jun 2014 14:04:28 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, Waiman.Long@...com,
	tglx@...utronix.de, mingo@...nel.org
CC:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	xen-devel@...ts.xenproject.org, kvm@...r.kernel.org,
	paolo.bonzini@...il.com, konrad.wilk@...cle.com,
	boris.ostrovsky@...cle.com, paulmck@...ux.vnet.ibm.com,
	riel@...hat.com, torvalds@...ux-foundation.org,
	raghavendra.kt@...ux.vnet.ibm.com, david.vrabel@...rix.com,
	oleg@...hat.com, gleb@...hat.com, scott.norton@...com,
	chegu_vinod@...com, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 10/11] qspinlock: Paravirt support

Il 15/06/2014 14:47, Peter Zijlstra ha scritto:
>
>
>  #if !defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE)
>
> -#define	queue_spin_unlock queue_spin_unlock
>  /**
>   * queue_spin_unlock - release a queue spinlock
>   * @lock : Pointer to queue spinlock structure
>   *
>   * An effective smp_store_release() on the least-significant byte.
>   */
> -static inline void queue_spin_unlock(struct qspinlock *lock)
> +static inline void native_queue_unlock(struct qspinlock *lock)
>  {
>  	barrier();
>  	ACCESS_ONCE(*(u8 *)lock) = 0;
>  }
>
> +#else
> +
> +static inline void native_queue_unlock(struct qspinlock *lock)
> +{
> +	atomic_dec(&lock->val);
> +}
> +
>  #endif /* !CONFIG_X86_OOSTORE && !CONFIG_X86_PPRO_FENCE */


Should be (part of) an earlier patch?  Also, does it get wrong if 
(CONFIG_X86_OOSTORE || CONFIG_X86_PPRO_FENCE) && paravirt patches the 
unlock to a single movb?  Of course the paravirt spinlocks could simply 
depend on !CONFIG_X86_OOSTORE && !CONFIG_X86_PPRO_FENCE.

> +
> +#define INVALID_HEAD	-1
> +#define NO_HEAD		nr_cpu_ids
> +

-2, like Waiman said.

Paolo
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