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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 09:34:40 +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 17.11.10 at 10:08, Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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.


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