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Date: Mon, 15 Nov 2010 11:39:03 -0800
From: Jeremy Fitzhardinge <jeremy@goop.org>
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To: Eric Dumazet <eric.dumazet@gmail.com>
CC: =?UTF-8?B?QW3DqXJpY28gV2FuZw==?= <xiyou.wangcong@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nick Piggin <npiggin@suse.de>, Jan Beulich <JBeulich@novell.com>,
        Avi Kivity <avi@redhat.com>, Xen-devel <xen-devel@lists.xensource.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Subject: Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock common
References: <cover.1288794124.git.jeremy.fitzhardinge@citrix.com>	 <4cea7b0804de5a2c1249034fc5c4840ade043ff4.1288794124.git.jeremy.fitzhardinge@citrix.com>	 <20101113101732.GH3837@hack> <1289645321.2743.21.camel@edumazet-laptop>
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On 11/13/2010 02:48 AM, Eric Dumazet wrote:
> Le samedi 13 novembre 2010 à 18:17 +0800, Américo Wang a écrit :
>> On Wed, Nov 03, 2010 at 10:59:47AM -0400, Jeremy Fitzhardinge wrote:
>>
>>> +	union {
>>> +		struct __raw_tickets tickets;
>>> +		__ticketpair_t slock;
>>> +	} tmp, new;
>>> +	int ret;
>>> +
>>> +	tmp.tickets = ACCESS_ONCE(lock->tickets);
>>> +	if (tmp.tickets.head != tmp.tickets.tail)
>>> +		return 0;
>>> +
>>> +	new.slock = tmp.slock + (1 << TICKET_SHIFT);
>>> +
>>> +	ret = cmpxchg(&lock->ticketpair, tmp.slock, new.slock) == tmp.slock;
>>> +	barrier();		/* just make nothing creeps before lock is claimed */
>> This one should be smp_wmb(), right? No CONFIG_X86_OOSTORE protected.
> cmpxchg() is a full memory barrier, no need for smp_wmb() or barrier()

Agreed.

    J