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Date: Wed, 17 Nov 2010 10:58:22 +0200
From: Avi Kivity <avi@redhat.com>
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To: Jeremy Fitzhardinge <jeremy@goop.org>
CC: Jan Beulich <JBeulich@novell.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        Eric Dumazet <dada1@cosmosbay.com>, xiyou.wangcong@gmail.com,
        Peter Zijlstra <peterz@infradead.org>, Nick Piggin <npiggin@kernel.dk>,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Xen-devel <xen-devel@lists.xensource.com>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
References: <cover.1289940821.git.jeremy.fitzhardinge@citrix.com><cover.1289940821.git.jeremy.fitzhardinge@citrix.com> <97ed99ae9160bdb6477284b333bd6708fb7a19cb.1289940821.git.jeremy.fitzhardinge@citrix.com> <4CE3A1060200007800022B04@vpn.id2.novell.com> <4CE397C8.9040901@goop.org>
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On 11/17/2010 10:52 AM, Jeremy Fitzhardinge wrote:
> On 11/17/2010 12:31 AM, Jan Beulich wrote:
> >>>>  On 16.11.10 at 22:08, Jeremy Fitzhardinge<jeremy@goop.org>  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?
>
> Actually in this case I'm pretty sure there's already a "set bit"
> function which will do the job.  set_bit(), I guess, though it takes a
> bit number rather than a mask...
>

set_bit() operates on a long, while the intel manuals recommend against 
operating on operands of different size, especially with locked 
operations.  I think newer processors have more relaxed requirements, 
though.

-- 
error compiling committee.c: too many arguments to function