From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1N68U0-0006Jj-CZ for qemu-devel@nongnu.org; Thu, 05 Nov 2009 14:59:00 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1N68Tv-0006Fw-HF for qemu-devel@nongnu.org; Thu, 05 Nov 2009 14:58:59 -0500 Received: from [199.232.76.173] (port=52955 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1N68Tv-0006Fs-4S for qemu-devel@nongnu.org; Thu, 05 Nov 2009 14:58:55 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.145]:50271) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1N68Tu-0001ws-Mz for qemu-devel@nongnu.org; Thu, 05 Nov 2009 14:58:54 -0500 Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by e5.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id nA5JmYWD003609 for ; Thu, 5 Nov 2009 14:48:34 -0500 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id nA5JwqsO1404940 for ; Thu, 5 Nov 2009 14:58:52 -0500 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id nA5Ft4ij026511 for ; Thu, 5 Nov 2009 10:55:04 -0500 Message-ID: <4AF32E78.1040103@us.ibm.com> Date: Thu, 05 Nov 2009 13:58:48 -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 Avi Kivity wrote: > 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. If this is such an issue, then it's something that ought to be fixed in the kernel. It's only really applicable to hotplug anyway as you wouldn't have faulted in the memory when initially launching the guest. I know this has been discussed before, but isn't this why there are things like vfork()? Instead of doing silly things into qemu, if there is concern about this, then it should be fixed in Linux properly. > I'd much prefer a small daemon serving taps on a unix-domain socket. > Of course, management should talk to that daemon, not qemu. I'd rather not have a program running with elevated privileges when it not needed. -- Regards, Anthony Liguori