Re: [Xen-devel] [PATCH] x86: adjust placement of pause insn in_raw_spin_lock()

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

That's the way it's done elsewhere and it's recommended (i.e. pause
immediately preceding the memory reference of the possibly contended
location). Jan

>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 08.08.08 15:12 >>>
Why?

 -- Keir

On 8/8/08 13:49, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
> 
> Index: 2008-08-06/xen/include/asm-x86/spinlock.h
> ===================================================================
> --- 2008-08-06.orig/xen/include/asm-x86/spinlock.h 2007-09-10
> 09:59:37.000000000 +0200
> +++ 2008-08-06/xen/include/asm-x86/spinlock.h 2008-08-07 12:36:13.000000000
> +0200
> @@ -23,8 +23,8 @@ static inline void _raw_spin_lock(spinlo
>          "1:  lock; decb %0         \n"
>          "    js 2f                 \n"
>          ".section .text.lock,\"ax\"\n"
> -        "2:  cmpb $0,%0            \n"
> -        "    rep; nop              \n"
> +        "2:  rep; nop              \n"
> +        "    cmpb $0,%0            \n"
>          "    jle 2b                \n"
>          "    jmp 1b                \n"
>          ".previous"
> 
> 
> 
> 
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