From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1N6Ci0-00065J-8T for qemu-devel@nongnu.org; Thu, 05 Nov 2009 19:29:44 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1N6Chv-0005wV-31 for qemu-devel@nongnu.org; Thu, 05 Nov 2009 19:29:43 -0500 Received: from [199.232.76.173] (port=33272 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1N6Chu-0005vb-W7 for qemu-devel@nongnu.org; Thu, 05 Nov 2009 19:29:39 -0500 Received: from e36.co.us.ibm.com ([32.97.110.154]:42989) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1N6Cht-0002FY-UL for qemu-devel@nongnu.org; Thu, 05 Nov 2009 19:29:38 -0500 Received: from d03relay03.boulder.ibm.com (d03relay03.boulder.ibm.com [9.17.195.228]) by e36.co.us.ibm.com (8.14.3/8.13.1) with ESMTP id nA60ROfF032737 for ; Thu, 5 Nov 2009 17:27:24 -0700 Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nA60TXCI146454 for ; Thu, 5 Nov 2009 17:29:33 -0700 Received: from d03av05.boulder.ibm.com (loopback [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id nA60TX8B023454 for ; Thu, 5 Nov 2009 17:29:33 -0700 Message-ID: <4AF36DE9.3040803@us.ibm.com> Date: Thu, 05 Nov 2009 18:29:29 -0600 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 0/4] net-bridge: rootless bridge support for qemu References: <1257294485-27015-1-git-send-email-aliguori@us.ibm.com> <20091105163702.GC21630@shareable.org> <4AF30129.7080203@us.ibm.com> <200911051820.48878.arnd@arndb.de> <4AF3154F.8090901@redhat.com> In-Reply-To: <4AF3154F.8090901@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Mark McLoughlin , Arnd Bergmann , Arnd Bergmann , Juan Quintela , Dustin Kirkland , qemu-devel@nongnu.org, Michael Tsirkin , Adam Litke Avi Kivity wrote: > On 11/05/2009 07:20 PM, Arnd Bergmann wrote: >> On Thursday 05 November 2009, Anthony Liguori wrote: >> >>>> It'd still install the default helper you've provided and use it by >>>> default, of course. >>>> >>>> >>> That's already how it behaves. You can say -net >>> bridge,helper=/usr/local/bin/my-helper >>> >>> >> How about abstracting it further and not making the helper depend on >> bridge code. If we put the helper into netcf, we could make that >> a more generic '-net netcf,helper=/usr/bin/netcf-helper' target, >> with netcf doing the correct thing for the system configuration, >> whether that is tap+bridge, tap+route, macvtap or something else >> coming up. The helper would essentially become a black box for >> providing a tap-like file descriptor with external connectivity. >> > > Helpers are really bad. On launch, I find the fragile and hard to do > proper error handling with (but that's probably just me). But the > real problem is at runtime, if you have a 16GB guest then you have to > write-protect 4M ptes and then kvm has to tear down or write protect > (not sure which mmu notifier is called) 4M shadow ptes. Once that's > done, the guest will have to fault its way back; that's at least 4M > exits, around 10 seconds worth of cpu time to execute a couple of > syscalls. FWIW, with large pages, it's only 8k exits which comes out to about 16ms. If nothing else, it's an argument for the important of transparent large pages. -- Regards, Anthony Liguori