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Mon, 6 Dec 2021 11:43:15 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C5AF242042; Mon, 6 Dec 2021 11:43:14 +0000 (GMT) Received: from p-imbrenda (unknown [9.145.0.173]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 6 Dec 2021 11:43:14 +0000 (GMT) Date: Mon, 6 Dec 2021 12:43:12 +0100 From: Claudio Imbrenda To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Subject: Re: [PATCH v1 1/1] osdep: asynchronous teardown for shutdown on Linux Message-ID: <20211206124312.0a13b7c0@p-imbrenda> In-Reply-To: References: <20211206110611.27283-1-imbrenda@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-GUID: pM5ozM1A-UrV_CXf3AJI73q9tHY2Bgn7 X-Proofpoint-ORIG-GUID: YaK7rYFkzgrO1AR-tgQFXOrRtzgTRuiP X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.11.62.513 definitions=2021-12-06_04,2021-12-06_01,2021-12-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxlogscore=745 clxscore=1015 malwarescore=0 bulkscore=0 impostorscore=0 spamscore=0 suspectscore=0 mlxscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2112060069 Received-SPF: pass client-ip=148.163.156.1; envelope-from=imbrenda@linux.ibm.com; helo=mx0a-001b2d01.pphosted.com X-Spam_score_int: -19 X-Spam_score: -2.0 X-Spam_bar: -- X-Spam_report: (-2.0 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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: , Cc: thuth@redhat.com, frankja@linux.ibm.com, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, borntraeger@de.ibm.com, pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, 6 Dec 2021 11:21:10 +0000 Daniel P. Berrang=C3=A9 wrote: > On Mon, Dec 06, 2021 at 12:06:11PM +0100, Claudio Imbrenda wrote: > > This patch adds support for asynchronously tearing down a VM on Linux. > >=20 > > 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). > >=20 > > 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. > >=20 > > This patch implements a simple trick on Linux to allow qemu to return > > immediately, with the teardown of the VM being performed > > asynchronously. > >=20 > > If the new commandline option -async-teardown is used, a new process is > > spawned from qemu using the clone syscall, so that it will share its > > address space with qemu. > >=20 > > The new process will then wait until qemu terminates, and then it will > > exit itself. > >=20 > > 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. > >=20 > > The teardown process will share the same cgroups as qemu, so both > > memory usage and cpu time will be accounted properly. =20 >=20 > If this suggested workaround has any benefit to the shutdown of a VM > with libvirt, then it is a bug in libvirt IMHO. >=20 > When libvirt tears down a QEMU VM, it should be waiting for *every* > process in the VM's cgroup to be terminated before it reports that > the VM is shutoff. IOW, the fact that this workaround lets the main > QEMU process exit quickly should not matter. libvirt should still > be blocked in exactly the same place in its code, waiting for the > "async" cleanup process to exit. IOW, this should not be async at > all from libvirt's POV. interesting, I did not know that about libvirt. maybe libvirt could be fixed/improved to allow this patch to work? surely without this patch an asynchronous teardown will not be possible at all >=20 >=20 > Regards, > Daniel