linux-kernel - Re: [PATCH 3/8] x86/ticketlock: Use C for __ticket_spin

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Date:	Fri, 24 Jun 2011 14:52:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 3/8] x86/ticketlock: Use C for __ticket_spin_unlock

On 06/23/2011 06:19 PM, Jeremy Fitzhardinge wrote:
> 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 f48a6e3..704b0c3 100644
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -33,9 +33,21 @@
>   * 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");
> +

These should be asm volatile, I believe.

	-hpa
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