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Subject: Re: [PATCH 1/4, v2] x86: enlightenment for ticket spin locks -
 base implementation
From: Peter Zijlstra <peterz@infradead.org>
To: Jan Beulich <JBeulich@novell.com>
Cc: mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com,
       jeremy.fitzhardinge@citrix.com, Ky Srinivasan <KSrinivasan@novell.com>,
       linux-kernel@vger.kernel.org
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Date: Wed, 30 Jun 2010 10:24:23 +0200
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On Tue, 2010-06-29 at 15:31 +0100, Jan Beulich wrote:
> @@ -62,18 +110,20 @@ static __always_inline void __ticket_spi
>  {
>         short inc = 0x0100;
>  
> -       asm volatile (
> +       alternative_common(
>                 LOCK_PREFIX "xaddw %w0, %1\n"
>                 "1:\t"
>                 "cmpb %h0, %b0\n\t"
> -               "je 2f\n\t"
> +               "je 2f\n\t",
>                 "rep ; nop\n\t"
>                 "movb %1, %b0\n\t"
>                 /* don't need lfence here, because loads are in-order
> */
>                 "jmp 1b\n"
> -               "2:"
> -               : "+Q" (inc), "+m" (lock->slock)
> -               :
> +               "2:",
> +               ALTERNATIVE_TICKET_LOCK,
> +               X86_FEATURE_SPINLOCK_YIELD,
> +               ASM_OUTPUT2("+Q" (inc), "+m" (lock->slock)),
> +               [stub] "i" (virt_spin_lock_stub)
>                 : "memory", "cc");
>  }


Also, instead of obfuscating __ticket_spin_lock(), can't you provide a
whole alternative arch_spin_lock() implementation and switch between
that and whatever bat-shit these paravirt people come up with?