Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762022Ab0HFUW2 (ORCPT ); Fri, 6 Aug 2010 16:22:28 -0400 Received: from terminus.zytor.com ([198.137.202.10]:46801 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761974Ab0HFUW0 (ORCPT ); Fri, 6 Aug 2010 16:22:26 -0400 Message-ID: <4C5C6DCE.4020206@zytor.com> Date: Fri, 06 Aug 2010 13:17:18 -0700 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.7) Gecko/20100720 Fedora/3.1.1-1.fc13 Thunderbird/3.1.1 MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Jan Beulich , Peter Zijlstra , Xen-devel , Avi Kivity , Nick Piggin , Linux Kernel Mailing List Subject: Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C References: <1280761639.1923.213.camel@laptop> <4C56E1A1.6020005@goop.org> <4C5C1F80020000780000EA6D@vpn.id2.novell.com> <4C5C21E3.1020004@goop.org> In-Reply-To: <4C5C21E3.1020004@goop.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 919 Lines: 29 On 08/06/2010 07:53 AM, Jeremy Fitzhardinge wrote: > 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. > A call/return to an actual out-of-line function is a barrier (and will always be a barrier, as it is the fundamental ABI sequence points), but to an inline function it is not. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/