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Thu, 9 Jul 2020 11:52:43 +0000 (UTC) Date: Thu, 9 Jul 2020 12:52:39 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH 2/2] util/qemu-sockets: make keep-alive enabled by default Message-ID: <20200709115239.GL3753300@redhat.com> References: <20200708191540.28455-1-vsementsov@virtuozzo.com> <20200708191540.28455-3-vsementsov@virtuozzo.com> <20200709082954.GD3753300@redhat.com> <62e64c31-1f6b-f27e-82ca-dfb3085a9869@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: <62e64c31-1f6b-f27e-82ca-dfb3085a9869@virtuozzo.com> User-Agent: Mutt/1.14.3 (2020-06-14) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/09 01:47:04 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: den@openvz.org, kraxel@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jul 09, 2020 at 11:49:17AM +0300, Vladimir Sementsov-Ogievskiy wrote: > 09.07.2020 11:29, Daniel P. Berrangé wrote: > > On Wed, Jul 08, 2020 at 10:15:39PM +0300, Vladimir Sementsov-Ogievskiy wrote: > > > Keep-alive won't hurt, let's try to enable it even if not requested by > > > user. > > > > Keep-alive intentionally breaks TCP connections earlier than normal > > in face of transient networking problems. > > > > The question is more about which type of pain is more desirable. A > > stall in the network connection (for a potentially very long time), > > or an intentionally broken socket. > > > > I'm not at all convinced it is a good idea to intentionally break > > /all/ QEMU sockets in the face of transient problems, even if the > > problems last for 2 hours or more. > > > > I could see keep-alives being ok on some QEMU socket. For example > > VNC/SPICE clients, as there is no downside to proactively culling > > them as they can trivially reconnect. Migration too is quite > > reasonable to use keep alives, as you generally want migration to > > run to completion in a short amount of time, and aborting migration > > needs to be safe no matter what. > > > > Breaking chardevs or block devices or network devices that use > > QEMU sockets though will be disruptive. The only solution once > > those backends have a dead socket is going to be to kill QEMU > > and cold-boot the VM again. > > > > Reasonable, thanks for explanation. > > We are mostly interested in keep-alive for migration and NBD connections. > (NBD driver has ability to reconnect). What do you think about setting > keep-alive (with some KEEPIDLE smaller than 2 hours) by default for > migration and NBD (at least when NBD reconnect is enabled), would it be > valid? I think it should be reasonable to set by default for those particular scenarios, as both are expecting failures and ready to take action when they occur. 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 :|