linux-kernel - Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C

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Message-ID: <4C5C21E3.1020004@goop.org>
Date:	Fri, 06 Aug 2010 07:53:23 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Jan Beulich <JBeulich@...ell.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Avi Kivity <avi@...hat.com>, Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C

  On 08/06/2010 05:43 AM, Jan Beulich wrote:
> You certainly mean "the compiler currently treats this as being:" - I
> don't think there's a guarantee it'll always be doing so.
>
>> 	for (;;) {
>> 		if (inc.tickets.head == inc.tickets.tail)
>> 			goto out;
>> 		...
>> 	}
>> out:	barrier();
>> }
>>
>> (Which would probably be a reasonable way to clarify the code.)
> I therefore think it needs to be written this way.

Agreed.

     J
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