From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 54CD4C19F2A for ; Thu, 4 Aug 2022 17:09:13 +0000 (UTC) Received: from localhost ([::1]:41732 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oJeLP-0005Ik-CH for qemu-devel@archiver.kernel.org; Thu, 04 Aug 2022 13:09:12 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:44632) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJeBH-0004Xw-VE for qemu-devel@nongnu.org; Thu, 04 Aug 2022 12:58:44 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:40807) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJeBF-0005IZ-NP for qemu-devel@nongnu.org; Thu, 04 Aug 2022 12:58:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659632321; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=aR8xs5bd6P9ja4ys4QiyEAgvnb7VUSRqAnhscfNEflU=; b=LIsXEb9+ixLpVUnzLT2T/ptzFEpuoxuiJMCTrhVtI9JD8ky1xxiYepJoDgoUkK5eVyGAs5 5AfvmVCvz2dChGkIngb8aYInkgZuvBWzEUS4cpETNSgHnqYjBoCTsFw/Xq0floI+N1QPD+ 6qeqS7cbO/JTaUhYJozpAEsVWgXHGmI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-549-0qS0muJLNvino3ObKOp07Q-1; Thu, 04 Aug 2022 12:58:39 -0400 X-MC-Unique: 0qS0muJLNvino3ObKOp07Q-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 543FF811E75; Thu, 4 Aug 2022 16:58:39 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.223]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 006392166B26; Thu, 4 Aug 2022 16:58:36 +0000 (UTC) Date: Thu, 4 Aug 2022 17:58:34 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Claudio Imbrenda , pbonzini@redhat.com, qemu-devel@nongnu.org, david@redhat.com, cohuck@redhat.com, thuth@redhat.com, borntraeger@de.ibm.com, frankja@linux.ibm.com, alex.bennee@linaro.org Subject: Re: [PATCH v2 1/1] osdep: asynchronous teardown for shutdown on Linux Message-ID: References: <20220803173141.52711-1-imbrenda@linux.ibm.com> <20220804075649.6e562c52@p-imbrenda> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.6 (2022-06-05) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Aug 04, 2022 at 09:20:59AM +0100, Daniel P. Berrangé wrote: > On Thu, Aug 04, 2022 at 07:56:49AM +0200, Claudio Imbrenda wrote: > > On Wed, 3 Aug 2022 18:34:45 +0100 > > Daniel P. Berrangé wrote: > > > > > On Wed, Aug 03, 2022 at 07:31:41PM +0200, Claudio Imbrenda wrote: > > > > This patch adds support for asynchronously tearing down a VM on Linux. > > > > > > > > When qemu terminates, either naturally or because of a fatal signal, > > > > the VM is torn down. If the VM is huge, it can take a considerable > > > > amount of time for it to be cleaned up. In case of a protected VM, it > > > > might take even longer than a non-protected VM (this is the case on > > > > s390x, for example). > > > > > > > > Some users might want to shut down a VM and restart it immediately, > > > > without having to wait. This is especially true if management > > > > infrastructure like libvirt is used. > > > > > > > > This patch implements a simple trick on Linux to allow qemu to return > > > > immediately, with the teardown of the VM being performed > > > > asynchronously. > > > > > > > > If the new commandline option -async-teardown is used, a new process is > > > > spawned from qemu at startup, using the clone syscall, in such way that > > > > it will share its address space with qemu. > > > > > > > > The new process will then simpy wait until qemu terminates, and then it > > > > will exit itself. > > > > > > > > This allows qemu to terminate quickly, without having to wait for the > > > > whole address space to be torn down. The teardown process will exit > > > > after qemu, so it will be the last user of the address space, and > > > > therefore it will take care of the actual teardown. > > > > > > > > The teardown process will share the same cgroups as qemu, so both > > > > memory usage and cpu time will be accounted properly. > > > > > > > > This feature can already be used with libvirt by adding the following > > > > to the XML domain definition: > > > > > > > > > > > > > > > > > > > > > > How does this work in practice ? Libvirt should be blocking until > > > > I don't know the inner details of how libvirt works.. > > > > > all processes in the cgroup have exited, including this cloned > > > child process. > > > > ..but I tested it and it works > > > > my impression is that libvirt by default is only waiting for the > > main qemu process. > > If true, that would be a bug that needs fixing and should not be > relied on. Libvirt is invoking 'TerminateMachine' DBus call on systemd-machined. That in turn iterates over every process in the cgroup and kills them off. Docs are a little vague and I've not followed the code perfectly, but that should mean TeminateMachine doesnt return until every process in the cgroup has exited. That said, since this is a dbus API call, libvirt will probably timeout waiting for the DBus reply after something like 30-60 seconds IIRC. > > > the only issue I have found is the log file, which stays open as long > > as some file descriptors (which the cloned process inherits from the > > main qemu process) stay open. A new VM cannot be started if its log file > > is still open by the logger process. The close_range() call solves the > > issue. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|