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[Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

To: "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>
Subject: [Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Wed, 17 Nov 2010 08:31:50 +0000
Cc: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xiyou.wangcong@xxxxxxxxx, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
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>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> +static inline void __ticket_enter_slowpath(struct arch_spinlock *lock)
> +{
> +     if (sizeof(lock->tickets.tail) == sizeof(u8))
> +             asm (LOCK_PREFIX "orb %1, %0"
> +                  : "+m" (lock->tickets.tail)
> +                  : "i" (TICKET_SLOWPATH_FLAG) : "memory");
> +     else
> +             asm (LOCK_PREFIX "orw %1, %0"
> +                  : "+m" (lock->tickets.tail)
> +                  : "i" (TICKET_SLOWPATH_FLAG) : "memory");
> +}

Came only now to mind: Here and elsewhere, did you try using
%z0 to have gcc produce the opcode suffix character, rather
than having these somewhat ugly if()-s?

Jan


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