Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754121Ab0DSKsH (ORCPT ); Mon, 19 Apr 2010 06:48:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14278 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753899Ab0DSKsD (ORCPT ); Mon, 19 Apr 2010 06:48:03 -0400 Message-ID: <4BCC34DF.6030702@redhat.com> Date: Mon, 19 Apr 2010 13:47:59 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Peter Zijlstra CC: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti , Zachary Amsden Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock References: <1271356648-5108-1-git-send-email-glommer@redhat.com> <1271356648-5108-2-git-send-email-glommer@redhat.com> <4BCA026D.3070309@redhat.com> <4BCA02D1.2020608@redhat.com> <1271673836.1674.757.camel@laptop> In-Reply-To: <1271673836.1674.757.camel@laptop> Content-Type: text/plain; charset=UTF-8; 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: 1052 Lines: 36 On 04/19/2010 01:43 PM, Peter Zijlstra wrote: > >>> >>>> + >>>> cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src) >>>> { >>>> struct pvclock_shadow_time shadow; >>>> unsigned version; >>>> cycle_t ret, offset; >>>> + u64 last; >>>> >>>> >>>> + do { >>>> + last = last_value; >>>> >>> Otherwise, this assignment can see a partial update. >>> >> On a 32-bit guest, that is. >> > Right, do bear in mind that the x86 implementation of atomic64_read() is > terrifyingly expensive, it is better to not do that read and simply use > the result of the cmpxchg. > > atomic64_read() _is_ cmpxchg64b. Are you thinking of some clever implementation for smp i386? -- error compiling committee.c: too many arguments to function -- 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/