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xen-devel
[Xen-devel] Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock
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To: |
Américo Wang <xiyou.wangcong@xxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock common |
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From: |
Eric Dumazet <eric.dumazet@xxxxxxxxx> |
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Date: |
Sat, 13 Nov 2010 11:48:41 +0100 |
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Cc: |
Nick Piggin <npiggin@xxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Srivatsa, Linux, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx> |
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Sat, 13 Nov 2010 02:49:39 -0800 |
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<20101113101732.GH3837@hack> |
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References: |
<cover.1288794124.git.jeremy.fitzhardinge@xxxxxxxxxx> <4cea7b0804de5a2c1249034fc5c4840ade043ff4.1288794124.git.jeremy.fitzhardinge@xxxxxxxxxx> <20101113101732.GH3837@hack> |
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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()
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