From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47452) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dAJxI-0007Q2-7I for qemu-devel@nongnu.org; Mon, 15 May 2017 13:38:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dAJxD-00007S-8Z for qemu-devel@nongnu.org; Mon, 15 May 2017 13:38:48 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40060) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dAJxC-00007H-VO for qemu-devel@nongnu.org; Mon, 15 May 2017 13:38:43 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id BD8E4AB99E for ; Mon, 15 May 2017 17:38:41 +0000 (UTC) Date: Mon, 15 May 2017 18:38:34 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170515173834.GI2089@work-vm> References: <20170512034033.GN28293@pxdev.xzpeter.org> <877f1mgx9h.fsf@secure.mitica> <5bab598f-30eb-fcf6-9d06-8f683b466414@redhat.com> <87lgpyfo28.fsf@secure.mitica> <87k25iqf4m.fsf@dusky.pond.sub.org> <87efvqdqqj.fsf@secure.mitica> <20170515163841.GB2324@work-vm> <87a86edpot.fsf@secure.mitica> <20170515172736.GA26717@work-vm> <871srqdnvw.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <871srqdnvw.fsf@secure.mitica> Subject: Re: [Qemu-devel] [PATCH 2/3] migration: Remove use of old MigrationParams List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: Markus Armbruster , Eric Blake , lvivier@redhat.com, qemu-devel@nongnu.org, Peter Xu * Juan Quintela (quintela@redhat.com) wrote: > "Dr. David Alan Gilbert" wrote: > > * Juan Quintela (quintela@redhat.com) wrote: > >> "Dr. David Alan Gilbert" wrote: > >> > * Juan Quintela (quintela@redhat.com) wrote: > >> >> Markus Armbruster wrote: > >> >> > Juan Quintela writes: > >> >> > > >> >> >> Eric Blake wrote: > >> >> > >> >> > >> >> >>> Or is the proposal that we are also going to simplify the QMP 'migrate' > >> >> >>> command to get rid of crufty parameters? > >> >> >> > >> >> >> I didn't read it that way, but I would not oppose O:-) > >> >> >> > >> >> >> Later, Juan. > >> >> > > >> >> > I'm not too familiar with this stuff, so please correct my > >> >> > misunderstandings. > >> >> > > >> >> > "Normal" migration configuration is global state, i.e. it applies to all > >> >> > future migrations. > >> >> > > >> >> > Except the "migrate" command's flags apply to just the migration kicked > >> >> > off by that command. > >> >> > > >> >> > QMP command "migrate" has two flags "blk" (HMP: -b) and "inc" (HMP: -i). > >> >> > !blk && inc makes no sense and is silently treated like !blk && !inc. > >> >> > > >> >> > There's a third flag "detach" (HMP: -d), but it does nothing in QMP. > >> >> > >> >> As qmp command is asynchronous, you can think that -d is *always* on in > >> >> QMP O:-) > >> >> > >> >> > You'd like to deprecate these flags in favour of "normal" configuration. > >> >> > However, we need to maintain QMP backward compatibility at least for a > >> >> > while. HMP backward compatibility is nice to have, but not required. > >> >> > > >> >> > First step is to design the new interface you want. Second step is to > >> >> > figure out backward compatibility. > >> >> > > >> >> > The new interface adds a block migration tri-state (off, > >> >> > non-incremental, incremental) to global state, default off. Whether > >> >> > it's done as two bools or an enum of three values doesn't matter here. > >> >> > >> >> Tristates will complicate it. I still think that: > >> >> > >> >> - capability: block_migration > >> >> - parameter: block_shared > >> >> > >> >> Makes more sense, no? > >> > > >> > I don't understand what making block_shared a parameter gives you as > >> > opposed to simply having two capabilities. > >> > > >> > (And how did we get 'shared'? We started off with block & incremental) > >> > >> The variables on MigrationParams: > >> > >> struct MigrationParams { > >> bool blk; > >> bool shared; > >> }; > >> > >> > >> I can move to incremental. I am not sure which one is clearer. > >> > >> The advantage of having shared as a parameter is that we forget about > >> all this dependency bussiness. Is the same than compression_threads > >> paramter, you setup to whichever value that you want. But you don't get > >> compression_threads until you set the compress capability. > >> > >> So, in this case we will have: > >> > >> block capability: Are we using block migration or not > >> block-incremental parameter: If we are using block migration, are we > >> using incremental copying of the block layer? > > > > If it's still a boolean why does having it as a parameter remove the > > dependency? > > Forget -b/-i. > > migration_set_parameter compression_threads 8 > > migrate > > We don't use compression_threads at all > > migrate_set_capability compress > > migrate > > Now, we use compression threads. > > So, compression_threads parameter is a parameter that is only used when > compress capability is enabled. > > Same for block migration. Block_incremental parameter is used only when > block migration capability is setup. No dependency check needed at all. > > Or I am losing something obvious here? Ah, you've made up a new rule - I don't think it's a bad rule but is it true? Do we always enable a capability before we use a parameter? I don't think so - I think the tls parameters don't have a capability. My previous rule was just that if it was a bool it was a capability and you can have whatever dependencies you like there - or none. Dave > Later, Juan. -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK