From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753332Ab0INJ1c (ORCPT ); Tue, 14 Sep 2010 05:27:32 -0400 Received: from mx1.redhat.com ([209.132.183.28]:61639 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752283Ab0INJ1a (ORCPT ); Tue, 14 Sep 2010 05:27:30 -0400 Message-ID: <4C8F3FF3.9080803@redhat.com> Date: Tue, 14 Sep 2010 11:27:15 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100907 Fedora/3.1.3-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.3 MIME-Version: 1.0 To: Jan Kiszka CC: Zachary Amsden , kvm@vger.kernel.org, Marcelo Tosatti , Glauber Costa , Thomas Gleixner , John Stultz , linux-kernel@vger.kernel.org Subject: Re: [KVM timekeeping 10/35] Fix deep C-state TSC desynchronization References: <1282291669-25709-1-git-send-email-zamsden@redhat.com> <1282291669-25709-11-git-send-email-zamsden@redhat.com> <4C8F3C03.50306@siemens.com> In-Reply-To: <4C8F3C03.50306@siemens.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/14/2010 11:10 AM, Jan Kiszka wrote: > Am 20.08.2010 10:07, Zachary Amsden wrote: >> When CPUs with unstable TSCs enter deep C-state, TSC may stop >> running. This causes us to require resynchronization. Since >> we can't tell when this may potentially happen, we assume the >> worst by forcing re-compensation for it at every point the VCPU >> task is descheduled. >> >> Signed-off-by: Zachary Amsden >> --- >> arch/x86/kvm/x86.c | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >> index 7fc4a55..52b6c21 100644 >> --- a/arch/x86/kvm/x86.c >> +++ b/arch/x86/kvm/x86.c >> @@ -1866,7 +1866,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >> } >> >> kvm_x86_ops->vcpu_load(vcpu, cpu); >> - if (unlikely(vcpu->cpu != cpu)) { >> + if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) { >> /* Make sure TSC doesn't go backwards */ >> s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 : >> native_read_tsc() - vcpu->arch.last_host_tsc; > For yet unknown reason, this commit breaks Linux guests here if they are > started with only a single VCPU. They hang during boot, obviously no > longer receiving interrupts. > > I'm using kvm-kmod against a 2.6.34 host kernel, so this may be a side > effect of the wrapping, though I cannot imagine how. > > Anyone any ideas? > > Most likely, time went backwards, and some 'future - past' calculation resulted in a negative sleep value which was then interpreted as unsigned and resulted in a 2342525634 year sleep. Does your guest use kvmclock, tsc, or some other time source? -- error compiling committee.c: too many arguments to function