From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36429) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dlAZc-0006gU-0h for qemu-devel@nongnu.org; Fri, 25 Aug 2017 05:06:40 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dlAZY-00037w-Sl for qemu-devel@nongnu.org; Fri, 25 Aug 2017 05:06:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41788) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dlAZY-00036Q-M3 for qemu-devel@nongnu.org; Fri, 25 Aug 2017 05:06:36 -0400 Date: Fri, 25 Aug 2017 10:06:27 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170825090626.GA2090@work-vm> References: <1503471071-2233-1-git-send-email-peterx@redhat.com> <1503471071-2233-5-git-send-email-peterx@redhat.com> <20170823174411.GG2648@work-vm> <20170825053526.GE14174@pxdev.xzpeter.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170825053526.GE14174@pxdev.xzpeter.org> Subject: Re: [Qemu-devel] [RFC v2 4/8] QAPI: new QMP command option "without-bql" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: qemu-devel@nongnu.org, Paolo Bonzini , "Daniel P . Berrange" , Fam Zheng , Juan Quintela , mdroth@linux.vnet.ibm.com, Eric Blake , Laurent Vivier , Markus Armbruster * Peter Xu (peterx@redhat.com) wrote: > On Wed, Aug 23, 2017 at 06:44:12PM +0100, Dr. David Alan Gilbert wrote: > > [...] > > > > +Most of the commands require the Big QEMU Lock (BQL) be held during > > > +execution. However, there is a small subset of the commands that may > > > +not really need BQL at all. To mark out this kind of commands, we can > > > +specify "without-bql" to "true". This parameter is only a hint for > > > +internal QMP implementation to provide possiblility to allow commands > > > +be run in parallel, or reduce the contention of the lock. Users of QMP > > > +should not really be aware of such information. > > > > Well, I think users of these commands might select them specifically > > because they know that they won't block. Those who care about latency might > > look to use commands that don't take the lock because of a reduced > > effect on the performance as well. > > What would be the best way to tell user? I think again this should > mostly for HMP only, right? It needs to be docuemnted for QMP users as well so that those developing management code know what's safe. > Maybe we can add a new command to list these lock-free commands. Or, > I can dump something in "help" and "help info" like: > > (qemu) help migrate_incoming > migrate_incoming uri -- Continue an incoming migration from an -incoming defer (BQL-less) 'lock free' might be better? Dave > > -- > Peter Xu -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK