From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/5 V5] Avoid soft lockup message when KVM is stopped by host Date: Wed, 14 Dec 2011 17:08:36 +0200 Message-ID: <4EE8BBF4.8070108@redhat.com> References: <1323116344-17911-1-git-send-email-emunson@mgebm.net> <4EDF7B0D.4060001@redhat.com> <20111208151929.GA6301@mgebm.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: mingo@redhat.com, hpa@zytor.com, arnd@arndb.de, ryanh@linux.vnet.ibm.com, aliguori@us.ibm.com, mtosatti@redhat.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 To: Eric B Munson Return-path: Received: from mx1.redhat.com ([209.132.183.28]:31115 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757264Ab1LNPIx (ORCPT ); Wed, 14 Dec 2011 10:08:53 -0500 In-Reply-To: <20111208151929.GA6301@mgebm.net> Sender: kvm-owner@vger.kernel.org List-ID: On 12/08/2011 05:19 PM, Eric B Munson wrote: > > error compiling committee.c: too many arguments to function > > > My concern for preempt notifiers is masking real soft lockup warnings. If the > flag is set every time the vm is preempted, it becomes more likely that we will > mask real warnings. The ioctl was choosen because it sets the flag only when > the guest is being paused deliberately. > > AFAIK, SIGSTOP is not a supported way to stop a qemu vm so a soft lockup This is a kvm patch, not a qemu patch. In general we try to address general requirements, not just those that are specific to one userspace, even if it is near to our hearts. > warning would be working as designed there. If that isn't the case, or if it > ever changes, we could always install a signal handler for SIGCONT that set the > flag before resuming the vm. > > Scheduling delays are also beyond the scope of this problem and I see the soft > lockup warning as appropriate in that case. I don't think you should see a guest softlockup if the host is overloaded. Nor should you see it due to a long live migration pause, or STOP/CONT. You should see a guest softlockup if it is spinning due to a guest bug, and not for any other reason. I think we need a mix of the ioctl (for STOP/CONT and voluntary pauses, like live migration or qemu stop/cont) and preempt notifiers (together with a check for TASK_RUNNING/TASK_UNINTERRUPTIBLE, for scheduling or swap delays) -- error compiling committee.c: too many arguments to function