From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by host Date: Mon, 19 Dec 2011 15:50:47 -0200 Message-ID: <20111219175047.GA17347@amt.cnet> References: <1323116344-17911-1-git-send-email-emunson@mgebm.net> <4EDF7B0D.4060001@redhat.com> <20111214121622.GB18317@amt.cnet> <4EE8B53C.6070502@redhat.com> <20111214182101.GB21945@amt.cnet> <4EE9CA1C.3010801@redhat.com> <20111216093149.GA26982@amt.cnet> <4EEF351E.8040002@redhat.com> <20111219161108.GA15848@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20111219161108.GA15848@amt.cnet> Sender: kvm-owner@vger.kernel.org To: Avi Kivity Cc: Eric B Munson , mingo@redhat.com, hpa@zytor.com, arnd@arndb.de, ryanh@linux.vnet.ibm.com, aliguori@us.ibm.com, jeremy.fitzhardinge@citrix.com, levinsasha928@gmail.com, Jan Kiszka , kvm@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org List-Id: linux-arch.vger.kernel.org On Mon, Dec 19, 2011 at 02:11:08PM -0200, Marcelo Tosatti wrote: > On Mon, Dec 19, 2011 at 02:59:10PM +0200, Avi Kivity wrote: > > On 12/16/2011 11:31 AM, Marcelo Tosatti wrote: > > > > > > > > > > Slow enough that progress of the watchdog thread is unable to keep up > > > > > with timer interrupt processing. This is considered a hang and > > > > > should be reported. > > > > > > > > It's not a guest hang though! > > > > > > No, but your host system is in such a load state that for the sake of > > > system usability you better print out a warning message. > > > > What's the point in printing it in the guest? The guest can't observe > > host conditions. > > > > > I don't see the advantage of preempt notifiers over the simple, paravirt > > > solution proposed? Note kvmclock is already paravirt. > > > > Right. > > > > > What do you want to be done in preempt notifiers? Measure what to > > > consider setting this flag? > > > > Preemption while TASK_RUNNING or TASK_UNINTERRUPTIBLE. > > Maybe it is good (not sure), need to look into schedstats and think of > cases that would break legitimate guest hangs. And it probably also > affects the position of clearing the flag on the guest side as its > currently done in Eric's patchset. Is the task going to be TASK_UNINTERRUPTIBLE with SIGSTOP? Don't think so. Note "Preemption while TASK_RUNNING or TASK_UNINTERRUPTIBLE" is not functional for guest-paused-via-QEMU-monitor case. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:38878 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751974Ab1LSUoz (ORCPT ); Mon, 19 Dec 2011 15:44:55 -0500 Date: Mon, 19 Dec 2011 15:50:47 -0200 From: Marcelo Tosatti Subject: Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by host Message-ID: <20111219175047.GA17347@amt.cnet> References: <1323116344-17911-1-git-send-email-emunson@mgebm.net> <4EDF7B0D.4060001@redhat.com> <20111214121622.GB18317@amt.cnet> <4EE8B53C.6070502@redhat.com> <20111214182101.GB21945@amt.cnet> <4EE9CA1C.3010801@redhat.com> <20111216093149.GA26982@amt.cnet> <4EEF351E.8040002@redhat.com> <20111219161108.GA15848@amt.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111219161108.GA15848@amt.cnet> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Avi Kivity Cc: Eric B Munson , mingo@redhat.com, hpa@zytor.com, arnd@arndb.de, ryanh@linux.vnet.ibm.com, aliguori@us.ibm.com, jeremy.fitzhardinge@citrix.com, levinsasha928@gmail.com, Jan Kiszka , kvm@vger.kernel.org, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org Message-ID: <20111219175047.jgkj-0aV_BZg00iFrUeCMyKg9iR-D7ZSRTYTY5aafR0@z> On Mon, Dec 19, 2011 at 02:11:08PM -0200, Marcelo Tosatti wrote: > On Mon, Dec 19, 2011 at 02:59:10PM +0200, Avi Kivity wrote: > > On 12/16/2011 11:31 AM, Marcelo Tosatti wrote: > > > > > > > > > > Slow enough that progress of the watchdog thread is unable to keep up > > > > > with timer interrupt processing. This is considered a hang and > > > > > should be reported. > > > > > > > > It's not a guest hang though! > > > > > > No, but your host system is in such a load state that for the sake of > > > system usability you better print out a warning message. > > > > What's the point in printing it in the guest? The guest can't observe > > host conditions. > > > > > I don't see the advantage of preempt notifiers over the simple, paravirt > > > solution proposed? Note kvmclock is already paravirt. > > > > Right. > > > > > What do you want to be done in preempt notifiers? Measure what to > > > consider setting this flag? > > > > Preemption while TASK_RUNNING or TASK_UNINTERRUPTIBLE. > > Maybe it is good (not sure), need to look into schedstats and think of > cases that would break legitimate guest hangs. And it probably also > affects the position of clearing the flag on the guest side as its > currently done in Eric's patchset. Is the task going to be TASK_UNINTERRUPTIBLE with SIGSTOP? Don't think so. Note "Preemption while TASK_RUNNING or TASK_UNINTERRUPTIBLE" is not functional for guest-paused-via-QEMU-monitor case.