Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752931Ab0DWVbt (ORCPT ); Fri, 23 Apr 2010 17:31:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58954 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752998Ab0DWVbn (ORCPT ); Fri, 23 Apr 2010 17:31:43 -0400 Message-ID: <4BD211B9.5080707@redhat.com> Date: Fri, 23 Apr 2010 11:31:37 -1000 From: Zachary Amsden User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.8) Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3 MIME-Version: 1.0 To: Avi Kivity CC: Glauber Costa , Jeremy Fitzhardinge , 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> In-Reply-To: <4BD169B5.4000409@redhat.com> 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: 1278 Lines: 37 On 04/22/2010 11:34 PM, Avi Kivity wrote: > On 04/23/2010 04:44 AM, Zachary Amsden wrote: >> Or apply this patch. >> time-warp.patch >> >> >> 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. > Does lfence / mfence actually serialize? I thought there was some great confusion about that not being the case on all AMD processors, and possibly not at all on Intel. A trap, however is a great way to serialize. I think, there is no serializing instruction which can be used from userspace which does not trap, at least, I don't know one off the top of my head. Zach -- 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/