From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45533) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dl7HL-0004WQ-C8 for qemu-devel@nongnu.org; Fri, 25 Aug 2017 01:35:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dl7HI-0002nA-73 for qemu-devel@nongnu.org; Fri, 25 Aug 2017 01:35:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42678) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dl7HI-0002lD-0X for qemu-devel@nongnu.org; Fri, 25 Aug 2017 01:35:32 -0400 Date: Fri, 25 Aug 2017 13:35:26 +0800 From: Peter Xu Message-ID: <20170825053526.GE14174@pxdev.xzpeter.org> References: <1503471071-2233-1-git-send-email-peterx@redhat.com> <1503471071-2233-5-git-send-email-peterx@redhat.com> <20170823174411.GG2648@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170823174411.GG2648@work-vm> 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: "Dr. David Alan Gilbert" 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 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? 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) -- Peter Xu