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bh=7lFmPEXHuIdPeLZhc4N/39EKkEZEo1h2N2WS50iYrqU=; b=KohowiLHz/xucdXIzh6GKgGVokZFH7909tWf9kz//PbtP8XJuiTVRSDdWbqyGTNgKCXYaK XcF3iUJqsKQN4tx9mI6O5obQsDT0IN3b65QlhEF7RASb+V1cQeNTU94jYDs9hrVlpZMcOF 2zWq9iIaRvZkkfwLOxyPyXpHb3dyUvo= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-8-3mPdEluSOROBQCBUoq0Ybw-1; Tue, 09 Mar 2021 05:26:42 -0500 X-MC-Unique: 3mPdEluSOROBQCBUoq0Ybw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 93442800D55; Tue, 9 Mar 2021 10:26:41 +0000 (UTC) Received: from redhat.com (ovpn-114-154.ams2.redhat.com [10.36.114.154]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D5EC75D9DB; Tue, 9 Mar 2021 10:26:28 +0000 (UTC) Date: Tue, 9 Mar 2021 10:26:26 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Kevin Wolf Subject: Re: [PATCH v2] block/file-posix: Optimize for macOS Message-ID: References: <20210305121748.65173-1-akihiko.odaki@gmail.com> <20210309093718.GA5798@merkur.fritz.box> MIME-Version: 1.0 In-Reply-To: <20210309093718.GA5798@merkur.fritz.box> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.251, 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_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Fam Zheng , pkrempa@redhat.com, Stefan Hajnoczi , qemu-block@nongnu.org, qemu Developers , Markus Armbruster , Konstantin Nazarov , Akihiko Odaki , Max Reitz , John Snow , dgilbert@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Mar 09, 2021 at 10:37:18AM +0100, Kevin Wolf wrote: > Am 09.03.2021 um 05:52 hat Akihiko Odaki geschrieben: > > 2021年3月9日(火) 0:37 Akihiko Odaki : > > > > > > 2021年3月9日(火) 0:17 Stefan Hajnoczi : > > > > > > > > The live migration compatibility issue is still present. Migrating to > > > > another host might not work if the block limits are different. > > > > > > > > Here is an idea for solving it: > > > > > > > > Modify include/hw/block/block.h:DEFINE_BLOCK_PROPERTIES_BASE() to > > > > support a new value called "host". The default behavior remains > > > > unchanged for live migration compatibility but now you can use "host" if > > > > you know it's okay but don't care about migration compatibility. > > > > > > > > The downside to this approach is that users must explicitly say > > > > something like --drive ...,opt_io_size=host. But it's still better than > > > > the situation we have today where user must manually enter values for > > > > their disk. > > > > > > > > Does this sound okay to everyone? > > > > > > > > Stefan > > > > > > I wonder how that change affects other block drivers implementing > > > bdrv_probe_blocksizes. As far as I know, the values they report are > > > already used by default, which is contrary to the default not being > > > "host". > > > > > > Regards, > > > Akihiko Odaki > > > > Let me suggest a variant of Stefan's approach: > > > > Modify include/hw/block/block.h:DEFINE_BLOCK_PROPERTIES_BASE() to > > support a new value called "host". The default values for block size > > properties may be "host" or not, but they should be consistent. If > > they are "host" by default > > I'm not sure if it's a good idea, but maybe we could make it so that the > default is "host" only as long as you didn't specify -nodefaults? Then > libvirt would automatically keep the old behaviour (because it always > sets -nodefaults) and manual invocations would usually get the new one. > > Of course, when I start with "I'm not sure if it's a good idea", it's > usually not, but I wanted to share the thought anyway... Can you elaborate on what the actual live migration problem is, and its impact ? This patch is touching the block backends, so I'm wondering how backend data ends up having an impact on the migration stream which is all frontend device data ? I'm especially concerned by the mention that some block backends already have this problem, and wondering if it already impacts libvirt ? Using -nodefaults is good practice, but I'm still uncomfortable saying that its use is a requirement if you want migration to work, as that feels like a change in semantics for non-libvirt users (who can be mgmt apps, nor merely human interactive users). 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 :|