From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andre Przywara Subject: 2.6.35-rc1 regression with pvclock and smp guests Date: Thu, 22 Jul 2010 14:53:59 +0200 Message-ID: <4C483F67.1010007@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: Zachary Amsden , KVM list To: glommer@redhat.com Return-path: Received: from tx2ehsobe004.messaging.microsoft.com ([65.55.88.14]:53062 "EHLO TX2EHSOBE008.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751761Ab0GVM7g (ORCPT ); Thu, 22 Jul 2010 08:59:36 -0400 Sender: kvm-owner@vger.kernel.org List-ID: Hi, I found a regression with pvclock and SMP KVM _guests_. PVCLOCK enabled guest kernels boot with qemu-kvm.git and with smp=1, but with smp=2 halt at: Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled (last line shown) I bisected this down to: commit 489fb490dbf8dab0249ad82b56688ae3842a79e8 Author: Glauber Costa Date: Tue May 11 12:17:40 2010 -0400 x86, paravirt: Add a global synchronization point for pvclock One commit before works, smp=1 always works, disabling PVCLOCK works. Using qemu-kvm-0.12.4 works, too. Having PVCLOCK enabled and with smp=2 the kernel halts without any further message. This is still the case with the lastest tip. Even pinning both VCPU threads to the same host core show the bug. The bug triggers on all hosts I tested, an single socket quadcore Athlon, a dual socket dualcore K8-Opteron and a quad socket 12core Opteron. Please note that this is the guest kernel, the host kernel does not matter. I have no idea (and don't feel like ;-) debugging this, so I hope someone will find and fix the bug. Regards, Andre. -- Andre Przywara AMD-Operating System Research Center (OSRC), Dresden, Germany Tel: +49 351 448-3567-12