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Date: Wed, 17 Nov 2010 09:34:40 +0000
From: "Jan Beulich" <JBeulich@novell.com>
To: "Jeremy Fitzhardinge" <jeremy@goop.org>
Cc: "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>,
        "Avi Kivity" <avi@redhat.com>,
        "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>
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 <4CE398A0.3040105@goop.org> <4CE39B7A.1080706@goop.org>
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>>> On 17.11.10 at 10:08, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 11/17/2010 12:56 AM, Jeremy Fitzhardinge wrote:
>> On 11/17/2010 12:52 AM, Jeremy Fitzhardinge wrote:
>>> But, yes, %z0 sounds interesting.  Is it documented anywhere?  I think
>>> I've tried to use it in the past and run into gcc bugs.
>> This one: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39590 
>>
>> Should be OK in this case because there's no 64-bit values to be seen...
> Hm, it fails when __ticket_t is 16 bits:
> 
> /home/jeremy/git/linux/arch/x86/include/asm/spinlock.h: Assembler messages:
> /home/jeremy/git/linux/arch/x86/include/asm/spinlock.h:73: Error: suffix
> or operands invalid for `or'
> 
>         lock; ors $1, 2(%rbx)   #,
> 
> 
> So I don't think that's going to work out...

Indeed, it's only with 4.5 that non-float operands are properly
supported here. Sad.

Jan