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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id bd18sm14472816wmb.43.2021.11.29.06.50.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 29 Nov 2021 06:50:23 -0800 (PST) Date: Mon, 29 Nov 2021 14:50:21 +0000 From: "Dr. David Alan Gilbert" To: Li Zhang Subject: Re: [PATCH 1/2] multifd: use qemu_sem_timedwait in multifd_recv_thread to avoid waiting forever Message-ID: References: <20211126153154.25424-1-lizhang@suse.de> <20211126153154.25424-2-lizhang@suse.de> <50dbb2b9-152e-f97a-d82e-0b6613e54085@suse.de> MIME-Version: 1.0 In-Reply-To: <50dbb2b9-152e-f97a-d82e-0b6613e54085@suse.de> User-Agent: Mutt/2.1.3 (2021-09-10) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.717, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, 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: quintela@redhat.com, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-devel@nongnu.org, cfontana@suse.de Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Li Zhang (lizhang@suse.de) wrote: > > On 11/29/21 12:20 PM, Dr. David Alan Gilbert wrote: > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > > On Fri, Nov 26, 2021 at 04:31:53PM +0100, Li Zhang wrote: > > > > When doing live migration with multifd channels 8, 16 or larger number, > > > > the guest hangs in the presence of the network errors such as missing TCP ACKs. > > > > > > > > At sender's side: > > > > The main thread is blocked on qemu_thread_join, migration_fd_cleanup > > > > is called because one thread fails on qio_channel_write_all when > > > > the network problem happens and other send threads are blocked on sendmsg. > > > > They could not be terminated. So the main thread is blocked on qemu_thread_join > > > > to wait for the threads terminated. > > > Isn't the right answer here to ensure we've called 'shutdown' on > > > all the FDs, so that the threads get kicked out of sendmsg, before > > > trying to join the thread ? > > I agree a timeout is wrong here; there is no way to get a good timeout > > value. > > However, I'm a bit confused - we should be able to try a shutdown on the > > receive side using the 'yank' command. - that's what it's there for; Li > > does this solve your problem? > > No, I tried to register 'yank' on the receive side, the receive threads are > still waiting there. > > It seems that on send side, 'yank' doesn't work either when the send threads > are blocked. > > This may be not the case to call yank. I am not quite sure about it. We need to fix that; 'yank' should be able to recover from any network issue. If it's not working we need to understand why. > > > > multifd_load_cleanup already kicks sem_sync before trying to do a > > thread_join - so have we managed to trigger that on the receive side? > > There is no problem with sem_sync in function multifd_load_cleanup. > > But it is not called in my case, because no errors are detected on the > receive side. If you're getting TCP errors why aren't you seeing any errors on the receive side? > The problem is here: > > void migration_ioc_process_incoming(QIOChannel *ioc, Error **errp) > { >     MigrationIncomingState *mis = migration_incoming_get_current(); >     Error *local_err = NULL; >     bool start_migration; > >    ... > >     if (!mis->from_src_file) { > >     ... > >      } else { >         /* Multiple connections */ >         assert(migrate_use_multifd()); >         start_migration = multifd_recv_new_channel(ioc, &local_err); >         if (local_err) { >             error_propagate(errp, local_err); >             return; >         } >     } >    if (start_migration) { >         migration_incoming_process(); >     } > } > > start_migration is always 0, and migration is not started because some > receive threads are not created. > > No errors are detected here and the main process works well but receive > threads are all waiting for semaphore. > > It's hard to know if the receive threads are not created. If we can find a > way to check if any receive threads So is this only a problem for network issues that happen during startup, before all the threads have been created? Dave > are not created, we can kick the sem_sync and do cleanup. > > From the source code, the thread will be created when QIO channel detects > something by GIO watch if I understand correctly. > > If nothing is detected, socket_accept_icoming_migration won't be called, the > thread will not be created. > > socket_start_incoming_migration_internal -> > >     qio_net_listener_set_client_func_full(listener, > socket_accept_incoming_migration, >                                           NULL, NULL, > g_main_context_get_thread_default()); > >    qio_net_listener_set_client_func_full -> > >                qio_channel_add_watch_source( >                 QIO_CHANNEL(listener->sioc[i]), G_IO_IN, >                 qio_net_listener_channel_func, >                 listener, (GDestroyNotify)object_unref, context); > >   socket_accept_incoming_migration -> > >        migration_channel_process_incoming -> > >                migration_ioc_process_incoming -> > >                      multifd_recv_new_channel -> > >                             qemu_thread_create(&p->thread, p->name, > multifd_recv_thread, p, > QEMU_THREAD_JOINABLE); > > > > > Dave > > > > > 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 :| > > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK