From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753895AbbAEWJx (ORCPT ); Mon, 5 Jan 2015 17:09:53 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58338 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751684AbbAEWJw (ORCPT ); Mon, 5 Jan 2015 17:09:52 -0500 Date: Mon, 5 Jan 2015 14:09:50 -0800 From: Andrew Morton To: Cyril Bur Cc: linux-kernel@vger.kernel.org, mpe@ellerman.id.au, drjones@redhat.com, dzickus@redhat.com, mingo@kernel.org, uobergfe@redhat.com, chaiw.fnst@cn.fujitsu.com, cl@linu.com, fabf@skynet.be, atomlin@redhat.com, benzh@chromium.org Subject: Re: [PATCH 0/2] Quieten softlockup detector on virtualised kernels Message-Id: <20150105140950.9ef64425359c62475b48733d@linux-foundation.org> In-Reply-To: <1419224764-11384-1-git-send-email-cyrilbur@gmail.com> References: <1419224764-11384-1-git-send-email-cyrilbur@gmail.com> X-Mailer: Sylpheed 3.4.0beta7 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 22 Dec 2014 16:06:02 +1100 Cyril Bur wrote: > When the hypervisor pauses a virtualised kernel the kernel will observe a jump > in timebase, this can cause spurious messages from the softlockup detector. > > Whilst these messages are harmless, they are accompanied with a stack trace > which causes undue concern and more problematically the stack trace in the > guest has nothing to do with the observed problem and can only be misleading. > > Futhermore, on POWER8 this is completely avoidable with the introduction of > the Virtual Time Base (VTB) register. Does this problem apply to other KVM implementations and to Xen? If so, what would implementations of running_clock() for those look like? If not, why not?