From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:41562) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QjRtO-0000Nq-Nm for qemu-devel@nongnu.org; Wed, 20 Jul 2011 04:12:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QjRtM-0007eQ-TD for qemu-devel@nongnu.org; Wed, 20 Jul 2011 04:12:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:9394) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QjRtM-0007eK-Fx for qemu-devel@nongnu.org; Wed, 20 Jul 2011 04:12:28 -0400 Message-ID: <4E268DE5.90201@redhat.com> Date: Wed, 20 Jul 2011 11:12:21 +0300 From: Avi Kivity MIME-Version: 1.0 References: <1310901265-32051-1-git-send-email-avi@redhat.com> <4E2581F4.5090004@codemonkey.ws> <4E25864A.10905@redhat.com> <4E2599BC.9070407@codemonkey.ws> <4E25AB37.2030808@redhat.com> <4E25AC5D.1030205@redhat.com> <4E25EE3A.8030007@codemonkey.ws> <4E264344.1080505@codemonkey.ws> <1311142251.5871.8.camel@lappy> In-Reply-To: <1311142251.5871.8.camel@lappy> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC v4 00/58] Memory API List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Sasha Levin Cc: kvm@vger.kernel.org, qemu-devel@nongnu.org On 07/20/2011 09:10 AM, Sasha Levin wrote: > On Tue, 2011-07-19 at 21:53 -0500, Anthony Liguori wrote: > > QEMU does use it and it's quite important. Coalesced MMIO is really > > about write caching MMIO exits. It only works with devices that have > > registers where writing has no side effects. Moreover, it only really > > works well when there are lots and lots of writes to these registers > > simultaneously. > > > > Couple that with the fact that the buffer is a fixed size and it's > > really not flexible enough to be useful for a wide variety of devices. > > > > But for VGA planar mode writes, it works wonders. It would be terrible > > to totally lose it. That said, I'm not at all convinced it's useful for > > much other than VGA planar mode. > > Why was the coalesced approach taken in the first place? When I tried > using it for VGA in /tools/kvm it just seemed to me like a builtin > virtio-memory transport. > > Thats why I think planar VGA would be fine if we deprecate coalesced > mmio in favor of either socket ioeventfds or a new virtio-memory device. > virtio is guest visible. coealesced mmio is transparent to the guest. socket ioeventds also do coalescing, but they are more expensive to synchronize - you have to poll the socket whenever a synchronization event happens. -- error compiling committee.c: too many arguments to function