From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45229) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dptfU-0004Nb-7S for qemu-devel@nongnu.org; Thu, 07 Sep 2017 06:04:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dptfP-0001tQ-6p for qemu-devel@nongnu.org; Thu, 07 Sep 2017 06:04:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57822) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dptfO-0001tD-UM for qemu-devel@nongnu.org; Thu, 07 Sep 2017 06:04:11 -0400 Date: Thu, 7 Sep 2017 11:04:02 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170907100402.GG2098@work-vm> References: <1503471071-2233-1-git-send-email-peterx@redhat.com> <20170829110357.GG3783@redhat.com> <20170906094846.GA2215@work-vm> <20170906104603.GK15510@redhat.com> <20170906104850.GB2215@work-vm> <20170906105414.GL15510@redhat.com> <20170906105704.GC2215@work-vm> <20170906110629.GM15510@redhat.com> <20170906113157.GD2215@work-vm> <20170906115428.GP15510@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20170906115428.GP15510@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC v2 0/8] monitor: allow per-monitor thread List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Peter Xu , qemu-devel@nongnu.org, Paolo Bonzini , Fam Zheng , Juan Quintela , mdroth@linux.vnet.ibm.com, Eric Blake , Laurent Vivier , Markus Armbruster * Daniel P. Berrange (berrange@redhat.com) wrote: > On Wed, Sep 06, 2017 at 12:31:58PM +0100, Dr. David Alan Gilbert wrote: > > * Daniel P. Berrange (berrange@redhat.com) wrote: > > > This does imply that you need a separate monitor I/O processing, fr= om the > > > command execution thread, but I see no need for all commands to sud= denly > > > become async. Just allowing interleaved replies is sufficient from = the > > > POV of the protocol definition. This interleaving is easy to handle= from > > > the client POV - just requires a unique 'serial' in the request by = the > > > client, that is copied into the reply by QEMU. > >=20 > > OK, so for that we can just take Marc-Andr=E9's syntax and call it 'i= d': > > https://lists.gnu.org/archive/html/qemu-devel/2017-01/msg03634.html > >=20 > > then it's upto the caller to ensure those id's are unique. >=20 > Libvirt has in fact generated a unique 'id' for every monitor command > since day 1 of supporting QMP. >=20 > > I do worry about two things: > > a) With this the caller doesn't really know which commands could be > > in parallel - for example if we've got a recovery command that's > > executed by this non-locking thread that's OK, we expect that > > to be doable in parallel. If in the future though we do > > what you initially suggested and have a bunch of commands get > > routed to the migration thread (say) then those would suddenly > > operate in parallel with other commands that we're previously > > synchronous. >=20 > We could still have an opt-in for async commands. eg default to executi= ng > all commands in the main thread, unless the client issues an explicit > "make it async" command, to switch to allowing the migration thread to > process it async. >=20 > { "execute": "qmp_allow_async", > "data": { "commands": [ > "migrate_cancel", > ] } } >=20 >=20 > { "return": { "commands": [ > "migrate_cancel", > ] } } >=20 > The server response contains the subset of commands from the request > for which async is supported. >=20 > That gives good negotiation ability going forward as we incrementally > support async on more commands. Is that 'qmp_allow_async' a command purely to query whether a command is async or is it a wrapper to cause that command to be executed async? > > b) I still worry how the various IO channels will behave on another > > thread. But that's more a general feeling rather than anything > > specific. >=20 > The only complexity will be around making sure the Chardev code uses > the right GMainContext for any watches on the underlying QIOChannel, > so that we poll() from the custom thread instead of the main thread. > IOW, as long as all I/O is done from the single thread everything > should work fine. Dave > Regards, > Daniel > --=20 > |: https://berrange.com -o- https://www.flickr.com/photos/dberr= ange :| > |: https://libvirt.org -o- https://fstop138.berrange= .com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberr= ange :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK