Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755884Ab0DWT0A (ORCPT ); Fri, 23 Apr 2010 15:26:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33628 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752241Ab0DWTZ7 (ORCPT ); Fri, 23 Apr 2010 15:25:59 -0400 Message-ID: <4BD1F43E.2080404@redhat.com> Date: Fri, 23 Apr 2010 22:25:50 +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: Jeremy Fitzhardinge CC: Zachary Amsden , Glauber Costa , Peter Zijlstra , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Marcelo Tosatti Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock References: <1271675100.1674.818.camel@laptop> <4BCC3A3E.9070909@redhat.com> <20100419142158.GD14158@mothafucka.localdomain> <4BCC69D5.3050209@redhat.com> <1271688411.1488.248.camel@laptop> <4BCC8246.9040202@goop.org> <4BCD748E.7080007@redhat.com> <4BCDF12C.1020702@goop.org> <4BCDF85C.3000004@redhat.com> <4BCE0399.2010708@goop.org> <20100422131113.GA3364@mothafucka.localdomain> <4BD0FB92.4060301@redhat.com> <4BD169B5.4000409@redhat.com> <4BD1F37A.6040801@goop.org> In-Reply-To: <4BD1F37A.6040801@goop.org> 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: 1217 Lines: 35 On 04/23/2010 10:22 PM, Jeremy Fitzhardinge wrote: > On 04/23/2010 02:34 AM, Avi Kivity wrote: > >>> diff -rup a/time-warp-test.c b/time-warp-test.c >>> --- a/time-warp-test.c 2010-04-15 16:30:13.955981607 -1000 >>> +++ b/time-warp-test.c 2010-04-15 16:35:37.777982377 -1000 >>> @@ -91,7 +91,7 @@ static inline unsigned long long __rdtsc >>> { >>> DECLARE_ARGS(val, low, high); >>> >>> - asm volatile("cpuid; rdtsc" : EAX_EDX_RET(val, low, high)); >>> + asm volatile("cpuid; rdtsc" : EAX_EDX_RET(val, low, high) :: >>> "ebx", "ecx"); >>> >>> >>> >> >> Plus, replace cpuid by lfence/mfence. cpuid will trap. >> > I presume the clobbers are needed for cpuid; if you use [lm]fence then > they shouldn't be needed, right? > > Right. But I'm not sure lfence/mfence are sufficient - from what I understand rdtsc can pass right through them. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- 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/