linux-kernel - Re: [PATCH 03/20] x86/ticketlock: Use C for __ticket_spin

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Date:	Wed, 03 Nov 2010 16:13:38 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...e.de>,
	Jan Beulich <JBeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 03/20] x86/ticketlock: Use C for __ticket_spin_unlock

Le mercredi 03 novembre 2010 à 10:59 -0400, Jeremy Fitzhardinge a
écrit :
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> 
> If we don't need to use a locked inc for unlock, then implement it in C.
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> ---
>  arch/x86/include/asm/spinlock.h |   33 ++++++++++++++++++---------------
>  1 files changed, 18 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
> index 6711d36..082990a 100644
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -33,9 +33,23 @@
>   * On PPro SMP or if we are using OOSTORE, we use a locked operation to unlock
>   * (PPro errata 66, 92)
>   */
> -# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
> +static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
> +{
> +	if (sizeof(lock->tickets.head) == sizeof(u8))
> +		asm (LOCK_PREFIX "incb %0"
> +		     : "+m" (lock->tickets.head) : : "memory");
> +	else
> +		asm (LOCK_PREFIX "incw %0"
> +		     : "+m" (lock->tickets.head) : : "memory");
> +
> +}
>  #else
> -# define UNLOCK_LOCK_PREFIX
> +static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
> +{
> +	barrier();

technically speaking, it should be : smp_wmb()

> +	lock->tickets.head++;
> +	barrier();

Not sure you need this one.

> +}
>  #endif
>  

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