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Fri, 5 Aug 2022 07:33:01 +0000 (GMT) Received: from d06av24.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5ABEF42042; Fri, 5 Aug 2022 07:33:01 +0000 (GMT) Received: from p-imbrenda (unknown [9.145.4.149]) by d06av24.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 5 Aug 2022 07:33:01 +0000 (GMT) Date: Fri, 5 Aug 2022 08:59:42 +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: <20220805085942.2c5cbce1@p-imbrenda> In-Reply-To: References: <20220803173141.52711-1-imbrenda@linux.ibm.com> <20220804164929.2ae0d34e@p-imbrenda> 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-GUID: HPsUhpRLrNcb6xKI3-MODq2gbagSoIPw X-Proofpoint-ORIG-GUID: IGprqQpQs2x-qnoPvyg68f_r-4vbvIZt 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=2022-08-05_01,2022-08-04_02,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 phishscore=0 suspectscore=0 spamscore=0 adultscore=0 mlxlogscore=999 priorityscore=1501 lowpriorityscore=0 mlxscore=0 bulkscore=0 clxscore=1015 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2206140000 definitions=main-2208050036 Received-SPF: pass client-ip=148.163.158.5; envelope-from=imbrenda@linux.ibm.com; helo=mx0b-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 Thu, 4 Aug 2022 17:41:01 +0100 Daniel P. Berrang=C3=A9 wrote: > On Thu, Aug 04, 2022 at 04:49:29PM +0200, Claudio Imbrenda wrote: > > On Thu, 4 Aug 2022 09:29:39 +0100 > > Daniel P. Berrang=C3=A9 wrote: > >=20=20=20 > > > On Wed, Aug 03, 2022 at 06:34:45PM +0100, Daniel P. Berrang=C3=A9 wro= te:=20=20 > > > > On Wed, Aug 03, 2022 at 07:31:41PM +0200, Claudio Imbrenda wrote:= =20=20=20=20 > > > > > This patch adds support for asynchronously tearing down a VM on L= inux. > > > > >=20 > > > > > When qemu terminates, either naturally or because of a fatal sign= al, > > > > > 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 immediatel= y, > > > > > 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 re= turn > > > > > immediately, with the teardown of the VM being performed > > > > > asynchronously. > > > > >=20 > > > > > If the new commandline option -async-teardown is used, a new proc= ess is > > > > > spawned from qemu at startup, using the clone syscall, in such wa= y that > > > > > it will share its address space with qemu. > > > > >=20 > > > > > The new process will then simpy wait until qemu terminates, and t= hen 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 ex= it > > > > > 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 follo= wing > > > > > to the XML domain definition: > > > > >=20 > > > > > > > > > > > > > > > =20=20=20=20 > > > >=20 > > > > How does this work in practice ? Libvirt should be blocking until > > > > all processes in the cgroup have exited, including this cloned > > > > child process.=20=20=20=20 > > >=20 > > > Also, have you disabled use of seccomp with QEMU when testing this, > > > as the seccomp filter that libivrt enables is supposed to block > > > any use of clone() except for the creation of threads.=20=20 > >=20 > > it was just a vanilla libvirt 8.0.0 as found on ubuntu 22.04; I have no > > idea how it is configured by default=20=20 >=20 > Ok, so the reason it is working is because the extra process is > cloned() right in middle of processing argv. This is before the > seccomp filter is applied to the process, so clone() is not blocked. >=20 > One think I note about this in practice is that (unsurprisingly) > if you do a process listing, users now see 2 QEMU processes instead > of one. >=20 > I wonder if we should consider overwriting argv in the child > process with "[qemu async teardown]" to give users a hint as to > why this duplicate process exists. sounds like a good idea >=20 > With regards, > Daniel