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Thu, 4 Aug 2022 05:56:52 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A0111A404D; Thu, 4 Aug 2022 05:56:51 +0000 (GMT) Received: from p-imbrenda (unknown [9.145.8.197]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 4 Aug 2022 05:56:51 +0000 (GMT) Date: Thu, 4 Aug 2022 07:56:49 +0200 From: Claudio Imbrenda To: "Daniel P. =?UTF-8?B?QmVycmFuZ8Op?=" Cc: 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: <20220804075649.6e562c52@p-imbrenda> In-Reply-To: References: <20220803173141.52711-1-imbrenda@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 4.1.0 (GTK 3.24.34; x86_64-redhat-linux-gnu) Content-Type: text/plain; charset=UTF-8 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: x7ybEsm3BVxjrRXSlljMkGuaNA_b1ayG X-Proofpoint-GUID: gNg40lDPHHYN8kMPeMEFMVlu3A_atuzs Content-Transfer-Encoding: quoted-printable X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-08-04_01,2022-08-02_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 spamscore=0 clxscore=1015 bulkscore=0 malwarescore=0 mlxlogscore=976 mlxscore=0 priorityscore=1501 lowpriorityscore=0 impostorscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2206140000 definitions=main-2208040023 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, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 3 Aug 2022 18:34:45 +0100 Daniel P. Berrang=C3=A9 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. > >=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 at startup, using the clone syscall, in such way that > > it will share its address space with qemu. > >=20 > > The new process will then simpy 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 > > This feature can already be used with libvirt by adding the following > > to the XML domain definition: > >=20 > > > > > > =20=20 >=20 > 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. 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. >=20 > With regards, > Daniel