From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932197AbbAFCnz (ORCPT ); Mon, 5 Jan 2015 21:43:55 -0500 Received: from mail-pa0-f49.google.com ([209.85.220.49]:33850 "EHLO mail-pa0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751138AbbAFCnx (ORCPT ); Mon, 5 Jan 2015 21:43:53 -0500 Message-ID: <1420512220.2910.39.camel@cyril> Subject: Re: [PATCH 0/2] Quieten softlockup detector on virtualised kernels From: Cyril Bur To: Andrew Morton 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 Date: Tue, 06 Jan 2015 13:43:40 +1100 In-Reply-To: <20150105140950.9ef64425359c62475b48733d@linux-foundation.org> References: <1419224764-11384-1-git-send-email-cyrilbur@gmail.com> <20150105140950.9ef64425359c62475b48733d@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2015-01-05 at 14:09 -0800, Andrew Morton wrote: > 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? Yes the problem should appear on other KVM implementations, not really sure about Xen but I don't see why the problem wouldn't crop up. x86 do have a method for dealing with it in the softlockup detector, they've added a check in the softlockup using a paravirtualised clock where the guest can discover if it had been paused, Xen could be using too. It doesn't appear s390 do anything. Thanks, Cyril > >