linux-kernel - Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

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Date:	Wed, 17 Nov 2010 09:34:40 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Jeremy Fitzhardinge" <jeremy.fitzhardinge@...rix.com>,
	"Eric Dumazet" <dada1@...mosbay.com>, <xiyou.wangcong@...il.com>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Nick Piggin" <npiggin@...nel.dk>,
	"Srivatsa Vaddagiri" <vatsa@...ux.vnet.ibm.com>,
	"Linux Virtualization" <virtualization@...ts.linux-foundation.org>,
	"Xen-devel" <xen-devel@...ts.xensource.com>,
	"Mathieu Desnoyers" <mathieu.desnoyers@...ymtl.ca>,
	"Avi Kivity" <avi@...hat.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

>>> On 17.11.10 at 10:08, Jeremy Fitzhardinge <jeremy@...p.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

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