From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:44211) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TVLrh-000293-2D for qemu-devel@nongnu.org; Mon, 05 Nov 2012 07:33:21 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TVLrc-0003QA-B8 for qemu-devel@nongnu.org; Mon, 05 Nov 2012 07:33:16 -0500 Received: from mx1.redhat.com ([209.132.183.28]:16600) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TVLrc-0003Pz-3L for qemu-devel@nongnu.org; Mon, 05 Nov 2012 07:33:12 -0500 Message-ID: <5097B203.30207@redhat.com> Date: Mon, 05 Nov 2012 14:33:07 +0200 From: Avi Kivity MIME-Version: 1.0 References: <509627A2.3040509@web.de> <5096C044.7060504@redhat.com> <50975C27.5010906@web.de> <509774ED.6040104@redhat.com> <50977E1A.1070105@siemens.com> In-Reply-To: <50977E1A.1070105@siemens.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] memory: Reintroduce dirty flag to optimize changes on disabled regions List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Blue Swirl , qemu-devel On 11/05/2012 10:51 AM, Jan Kiszka wrote: > On 2012-11-05 09:12, Avi Kivity wrote: > > On 11/05/2012 08:26 AM, Jan Kiszka wrote: > >> On 2012-11-04 20:21, Avi Kivity wrote: > >>> On 11/04/2012 10:30 AM, Jan Kiszka wrote: > >>>> From: Jan Kiszka > >>>> > >>>> Cirrus is triggering this, e.g. during Win2k boot: Changes only on > >>>> disabled regions require no topology update when transaction depth drops > >>>> to 0 again. > >>> > >>> 817dcc5368988b0 (pci: give each device its own address space) mad this > >>> much worse by multiplying the number of address spaces. Each change is > >>> now evaluated N+2 times, where N is the number of PCI devices. It also > >>> causes a corresponding expansion in memory usage. > >> > >> I know... But this regression predates your changes, is already visible > >> right after 02e2b95fb4. > >> > >>> > >>> I want to address this by caching AddressSpaceDispatch trees with the > >>> key being the contents of the FlatView for that address space. This > >>> will drop the number of distinct trees to 2-4 (3 if some devices have > >>> PCI_COMMAND_MASTER disabled, 4 if the PCI address space is different > >>> from the cpu memory address space) but will fail if we make each address > >>> space different (for example filtering out the device's own BARs). > >>> > >>> If this change also improves cpu usage sufficiently, then it will be > >>> better than your patch, which doesn't recognize changes in an enabled > >>> region inside a disabled or hidden region. > >> > >> True, though the question is how common such scenarios are. This one > >> (cirrus with win2k) is already special. > >> > >>> In other words, your patch > >>> fits the problem at hand but isn't general. On the other hand my > >>> approach doesn't eliminate render_memory_region(), just the exec.c stuff > >>> and listener updates. So we need to understand where the slowness comes > >>> from. > >> > >> I would just like to have some even intermediate solution for 1.3. We > >> can still make it more perfect later on if required. > >> > > > > I think we should apply a v2 then, the more general optimizations will > > take some time. > > OK - what should v2 do differently? > As I noted, init and destroy cannot cause a topology update. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.